#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;
    int dp[n + 1][26];
    for (int i = 0; i < 26; i++) {
        dp[0][i] = 0;
    }
    dp[0][s[0] - 'a'] = 1;
    for (int i = 0; i < n; i++) {

        if (s[i] == s[n - 1])
            v.push_back(i);
        if (i > 1) {
            for (int j  = 0; j < 26; j++) {
                dp[i][j] = dp[i - 1][j];

            }
            dp[i][s[i] - 'a'] = dp[i - 1][s[i] - 'a'] + 1;
        }

    }

    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;
            int mal = v[i] - 1;
            int br = 0;
            for (int j = 0; j < 26; j++) {
                int ka = 0;
                if (mal == -1)
                    ka = dp[n - 1][j];
                else
                    ka = dp[n - 1][j] - dp[mal][j];
                if (ka%2)
                    br++;
                if (br>1)
                    break;
            }
            if (br > 1)
                continue;
            else {
                while (a < b) {
                    if (s[a] != s[b]) {
                        cc = false;
                        break;
                    }
                    a++;
                    b--;
                }
                if (cc) {
                    cout << v[i] << endl;
                    return 0;
                }
            }
        }
    }
    return 0;
}