#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cmath>
#define maxx 5050
using namespace std;
int i,j;
int lena;
int f[maxx][maxx];
string a,b;
int cgy(){
	freopen("palin.in","r",stdin);
	freopen("palin.out","w",stdout);
	cin>>lena>>b;
	a=b;
	reverse(b.begin(),b.end());
	for(i=1;i<=lena;i++){
		for(j=1;j<=lena;j++){
			if(a[i-1]==b[j-1]){
				f[i][j]=f[i-1][j-1]+1;
			}
			else{
				f[i][j]=max(f[i-1][j],f[i][j-1]);
			}
		}
	}
	cout<<lena-f[lena][lena]<<endl;
	return 0;
}
int wzy=cgy();
int main(){;}