ыыыы2

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cmath>

typedef long long ll;

const ll mod = 1e9 + 7;
const int p = 247;
std::vector<ll> pow_p = {1};
int n;

void hash_func(std::vector<ll> &hash, std::string &s) {
    hash.resize(n + 1, 0);
    for (int i = 1; i < n + 1; i++) {
        hash[i] = ((hash[i - 1] * p) % mod + s[i - 1]) % mod;
    }
}

ll get_hash(std::vector<ll> &hash, int l, int r) {
    return (hash[r] - (hash[l - 1] * pow_p[r - l + 1]) % mod + mod) % mod;
}

ll get_n_hash(std::vector<ll> &hash, int l, int r) {
    return get_hash(hash, l, r);
}

ll get_r_hash(std::vector<ll> &hash, int l, int r) {
    return get_hash(hash, n - r + 1, n - l + 1);
}

int main() {
#ifdef LOCAL
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
#endif
    std::cin >> n;
    std::string s;
    std::cin >> s;
    for (int i = 1; i < n + 1; i++)
        pow_p.push_back((pow_p[i - 1] * p) % mod);
    std::vector<ll> n_hash;
    std::vector<ll> r_hash;
    hash_func(n_hash, s);
    std::reverse(s.begin(), s.end());
    hash_func(r_hash, s);
    bool flag = false;
    for (int k = 0; k < n; k++) {
        ll h = ((get_n_hash(n_hash, k + 1, n) * pow_p[k]) % mod + get_n_hash(n_hash, 1, k)) % mod;
        if (h == get_r_hash(r_hash, 1, n)) {
            std::cout << k;
            return 0;
        }
    }
    std::cout << -1;
    return 0;
}