#include<bits/stdc++.h>
using namespace std;
using ll = long long;

#ifdef DEB
#define D if(1)
#else 
#define D if(0)
#endif

const int NMAX = 512345;

char in[NMAX];
ll ha[NMAX];
ll hb[NMAX];
int n;

ll p=41;
ll q=1000000007;

int main()
{
	scanf("%d %s",&n,in);
	ll mocp=1;
	for(int i=n-1;i>=0;i--)
	{
		ha[i]=(ha[i+1]*p+in[i])%q;
		hb[i]=(hb[i+1]+in[i]*mocp)%q;
		mocp=mocp*p%q;
	}
	for(int i=0;i<n;i++)
	{
		if(ha[i]==hb[i])
		{
			D printf("HKOL %d\n",i);
			for(int a=i,b=n-1;;a++,b--)
			{
				if(in[a]!=in[b]) break;
				if(a>=b)
				{
					printf("%d\n",i);
					return 0;
				}
			}

		}
	}
}