#include <iostream>

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;

    int a = 0;

    while (!isPalindrome(a, n - 1)) {


        a++;
    }

    cout << a << endl;

}