#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 main() {

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

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


}