/*
written by- Piyush Golani
language- c++
country- India
College- N.I.T Jamshedpur
*/
#include <cmath>
#include <ctime>
#include <iostream>
#include <string>
#include <vector>
#include<cstdio>
#include<sstream>
#include<algorithm>
#include<cstdlib>
#include<cstring>
#include<map>
#include<queue>
#include<cctype>
using namespace std;
#define pb push_back
#define all(s) s.begin(),s.end()
#define f(i,a,b) for(int i=a;i<b;i++)
#define F(i,a,b) for(int i=a;i>=b;i--)
#define PI 3.1415926535897932384626433832795
#define INF 2000000000
#define BIG_INF 7000000000000000000LL
#define mp make_pair
#define eps 1e-9
#define LL long long
#define si(n) scanf("%d",&n)
#define sll(n) scanf("%lld",&n)
#define mod 1000000007
#define mm 10000000

class PenguinPals {
public:
   int findMaximumMatching( string colors ) {
    bool f=false;
    int matches=0;
    while(!f && colors.size()>=2)
    {
        f=true;
        if(colors[0]==colors[colors.size()-1])
        {
            f=false;
            matches++;
            colors=colors.substr(1,colors.size()-2);
        }
        int i=0;
        while(i+1<colors.size())
        {
            if(colors[i]==colors[i+1])
            {
                f=false;
                matches++;
                colors=colors.substr(0,i)+colors.substr(i+2);
            }
            i++;
        }
    }
    if(colors.size()>1)
    {
        matches+=(colors.size()-2)/2;
    }
    return matches;
   }
};

// BEGIN CUT HERE
namespace moj_harness {
    int run_test_case(int);
	void run_test(int casenum = -1, bool quiet = false) {
		if (casenum != -1) {
			if (run_test_case(casenum) == -1 && !quiet) {
				cerr << "Illegal input! Test case " << casenum << " does not exist." << endl;
			}
			return;
		}

		int correct = 0, total = 0;
		for (int i=0;; ++i) {
			int x = run_test_case(i);
			if (x == -1) {
				if (i >= 100) break;
				continue;
			}
			correct += x;
			++total;
		}

		if (total == 0) {
			cerr << "No test cases run." << endl;
		} else if (correct < total) {
			cerr << "Some cases FAILED (passed " << correct << " of " << total << ")." << endl;
		} else {
			cerr << "All " << total << " tests passed!" << endl;
		}
	}

	int verify_case(int casenum, const int &expected, const int &received, clock_t elapsed) {
		cerr << "Example " << casenum << "... ";

		string verdict;
		vector<string> info;
		char buf[100];

		if (elapsed > CLOCKS_PER_SEC / 200) {
			sprintf(buf, "time %.2fs", elapsed * (1.0/CLOCKS_PER_SEC));
			info.push_back(buf);
		}

		if (expected == received) {
			verdict = "PASSED";
		} else {
			verdict = "FAILED";
		}

		cerr << verdict;
		if (!info.empty()) {
			cerr << " (";
			for (int i=0; i<(int)info.size(); ++i) {
				if (i > 0) cerr << ", ";
				cerr << info[i];
			}
			cerr << ")";
		}
		cerr << endl;

		if (verdict == "FAILED") {
			cerr << "    Expected: " << expected << endl;
			cerr << "    Received: " << received << endl;
		}

		return verdict == "PASSED";
	}

	int run_test_case(int casenum__) {
		switch (casenum__) {
		case 0: {
			string colors             = "RRBRBRBB";
			int expected__            = 3;

			clock_t start__           = clock();
			int received__            = PenguinPals().findMaximumMatching(colors);
			return verify_case(casenum__, expected__, received__, clock()-start__);
		}
		case 1: {
			string colors             = "RRRR";
			int expected__            = 2;

			clock_t start__           = clock();
			int received__            = PenguinPals().findMaximumMatching(colors);
			return verify_case(casenum__, expected__, received__, clock()-start__);
		}
		case 2: {
			string colors             = "BBBBB";
			int expected__            = 2;

			clock_t start__           = clock();
			int received__            = PenguinPals().findMaximumMatching(colors);
			return verify_case(casenum__, expected__, received__, clock()-start__);
		}
		case 3: {
			string colors             = "RBRBRBRBR";
			int expected__            = 4;

			clock_t start__           = clock();
			int received__            = PenguinPals().findMaximumMatching(colors);
			return verify_case(casenum__, expected__, received__, clock()-start__);
		}
		case 4: {
			string colors             = "RRRBRBRBRBRB";
			int expected__            = 5;

			clock_t start__           = clock();
			int received__            = PenguinPals().findMaximumMatching(colors);
			return verify_case(casenum__, expected__, received__, clock()-start__);
		}
		case 5: {
			string colors             = "R";
			int expected__            = 0;

			clock_t start__           = clock();
			int received__            = PenguinPals().findMaximumMatching(colors);
			return verify_case(casenum__, expected__, received__, clock()-start__);
		}
		case 6: {
			string colors             = "RBRRBBRB";
			int expected__            = 3;

			clock_t start__           = clock();
			int received__            = PenguinPals().findMaximumMatching(colors);
			return verify_case(casenum__, expected__, received__, clock()-start__);
		}
		case 7: {
			string colors             = "RBRBBRBRB";
			int expected__            = 4;

			clock_t start__           = clock();
			int received__            = PenguinPals().findMaximumMatching(colors);
			return verify_case(casenum__, expected__, received__, clock()-start__);
		}

		// custom cases

/*      case 8: {
			string colors             = ;
			int expected__            = ;

			clock_t start__           = clock();
			int received__            = PenguinPals().findMaximumMatching(colors);
			return verify_case(casenum__, expected__, received__, clock()-start__);
		}*/
/*      case 9: {
			string colors             = ;
			int expected__            = ;

			clock_t start__           = clock();
			int received__            = PenguinPals().findMaximumMatching(colors);
			return verify_case(casenum__, expected__, received__, clock()-start__);
		}*/
/*      case 10: {
			string colors             = ;
			int expected__            = ;

			clock_t start__           = clock();
			int received__            = PenguinPals().findMaximumMatching(colors);
			return verify_case(casenum__, expected__, received__, clock()-start__);
		}*/
		default:
			return -1;
		}
	}
}


int main(int argc, char *argv[]) {
	if (argc == 1) {
		moj_harness::run_test();
	} else {
		for (int i=1; i<argc; ++i)
			moj_harness::run_test(atoi(argv[i]));
	}
}
// END CUT HERE