#include <iostream>
using namespace std;


int main() {
	string input_s;
	int input_n;
	cin >> input_n;
	cin >> input_s;

	int size = input_n * 2;
	char* arr = new char[size];
	bool flag = true;
	int index;
	int cnt = 0;

	for (int a = 0; a < input_n; a++) {
		arr[a] = input_s[a];
		arr[a + input_n] = input_s[a];
	}



	for (int a = 0; a < input_n; a++) {

		if (input_s[a] == input_s[input_n - 1] && flag == true) {
			index = a;

			for (int b = index; b < index + input_n; b++) {
				if (arr[b] == input_s[input_n + index - b - 1]) {
					cnt++;
				}
			}

			if (cnt == input_n) {
				cout << index;
				flag = false;
			}
			index = 0;
			cnt = 0;
		}
		else if (flag == false) break;
	}

	if (flag == true) {
		cout << -1;
	}
	return 0;
}