#include <iostream>
#include <string>
#include <vector>
using namespace std;
typedef long long ll;
int main() {
    cin.sync_with_stdio(false);
    cin.tie();
    cout.tie();
    int n;
    cin >> n;
    string s;
    cin >> s;
    vector<int> v;
    for (int i = 0; i < n; i++) {
        if (s[i] == s[n - 1])
            v.push_back(i);
    }
    for (int i = 0; i < v.size(); i++) {
        if (s[v[i]] ==  s[n - 1]) {
            int b = n - 1;
            int a = v[i];
            bool cc = true;
            while (a < b) {
                if (s[a] != s[b]) {
                    cc = false;
                    break;
                }
                a ++;
                b--;
            }
            if (cc) {
                cout<<v[i]<<endl;
                return 0;
            }
        }
    }
    return 0;
}