#include<bits/stdc++.h>
using namespace std;
const int maxn=5010;
char a[maxn],b[maxn];int f[maxn][maxn],len1,len2,n;
inline void in(){
	freopen("palin.in","r",stdin);
	freopen("palin.out","w",stdout);
	scanf("%d",&n);
	scanf("%s",a+1);
	for (int i=1;i<=n;i++){
		b[n-i+1]=a[i];
	}
}
inline void dp(){
	for (int i=1;i<=n;i++){
		for (int j=1;j<=n;j++){
			if(a[i]==b[j]){
				f[i][j]=f[i-1][j-1]+1;
			}
			else{
				if (f[i-1][j]>f[i][j-1]) f[i][j]=f[i-1][j];
				else f[i][j]=f[i][j-1];
			}
		}
	}
}
inline void p(){
	printf("%d",n-f[n][n]);
}
int Main(){
	in();
	dp();
	p();
	return 0;
}
int main(){;}
int xlm=Main();