#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
int n;
char a[10000];
char b[5000],c[5000];
int main()
{
	freopen("palin.in","r",stdin);
	freopen("palin.out","w",stdout);
	memset(a,'-',sizeof(a));
	scanf("%d",&n);
	for(int i=1;i<=n;i++)scanf("%c",&a[i+2500]);
	int ufo,jia=0x7fffffff;
	for(int ha=2501;ha<=2500+n;ha++)
	{
		int i,j,l=0;
		int go=max(ha-2500,2500+n-ha);
		for(i=j=ha;;i++,j--)
		{
			if(i-j==2*go)break;
			if(a[i]!=a[j])l++;
		}
		if(l<jia)
			jia=l;
	}
	printf("%d",jia);
	return 0;
}