// iostream is too mainstream
#include <cstdio>
// bitch please
#include <iostream>
#include <algorithm>
#include <cstdlib>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <list>
#include <cmath>
#include <iomanip>
#define dibs reserve
#define OVER9000 123456789012345678LL
#define ALL_THE(CAKE,LIE) for(auto LIE =CAKE.begin(); LIE != CAKE.end(); LIE++)
#define tisic 47
#define soclose 1e-8
#define chocolate win
// so much chocolate
#define patkan 9
#define ff first
#define ss second
#define abs(x) ((x < 0)?-(x):x)
#define uint unsigned int
#define dbl long double
using namespace std;
// mylittledoge

int main() {
	cin.sync_with_stdio(0);
	cin.tie(0);
	string s;
	cin >> s;
	int t =0, o =0, ans1 =0, ans2 =0;
	for(int i =0; i < s.length(); i++) {
		if(s[i] == '2') t++;
		else o++;
		if(s[i] == '2') ans1 +=o;
		else ans2 +=t;}
	cout << min(ans1,ans2) << "\n";
	return 0;}

// look at my code
// my code is amazing