#include <iostream>
#include <string>
#include <vector>

using namespace std;

string::size_type KMP(const string& S, int begin, const string& pattern)
{
    vector<int> pf(pattern.length());
    pf[0] = 0;
    for (int k = 0, i = 1; i < pattern.length(); ++i) {
        while ((k > 0) && (pattern[i] != pattern[k])) k = pf[k - 1];
        if (pattern[i] == pattern[k]) k++;
        pf[i] = k;
    }
    for (int k = 0, i = begin; i < S.length(); ++i) {
        while ((k > 0) && (pattern[k] != S[i])) k = pf[k - 1];
        if (pattern[k] == S[i]) k++;
        if (k == pattern.length()) return (i - pattern.length() + 1);
    }
    return (string::npos);
}

int main()
{
    int n;
    string s, m;
    cin >> n >> s;
    for (int i = 0; i < n; i++) {
        m += s[n - i - 1];
    }
    s = s + s;

    string::size_type kmp_res = KMP(s, 0, m);
    if (kmp_res <= n) cout << kmp_res;
    else cout << - 1;
}