/*
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<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 1000000005
#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 MAX 5005
char A[MAX];
int L[2][MAX];
int n;
int ch()
{
f(i,1,n+1)
{
f(j,1,n+1)
{
if(A[i-1]==A[n-j])
{
L[i%2][j]=1+L[(i-1)%2][j-1];
}
else
{
L[i%2][j]=max(L[(i-1)%2][j],L[i%2][j-1]);
}
}
}
return L[n%2][n];
}
int main()
{
si(n);
scanf("%s",A);
//puts(B);
printf("%d\n",n-ch());
return 0;
}
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