#include <iostream>
#include <string>

using namespace std;

string str;
bool isPalindrome(int a, int b)  {

    if (a == b) return true;
    if (a + 1 == b) {
        if (str[a] == str[b]) return true;
    }

    if (str[a] != str[b]) return false;

    return isPalindrome(a + 1, b - 1);
}

int last_positions[400000];
int xd = 0;
int main() {

    int n;
    cin >> n >> str;
    string c = str;

    while (c.find(str[n - 1]) != string::npos) {
        last_positions[xd] = c.find(str[n - 1]);
        c = c.substr(last_positions[xd] + 1);
        xd++;
    }
 
    for (int i = 0; i < xd; i++) {
        if (isPalindrome(last_positions[i], n - 1));
        cout << last_positions[i] << endl;
        break;
    }

}