#include "iostream"
using namespace std;

int N;
int nyanpass[8] = { 'n','y','a','n','p','a','s','s' };
char greeting[100][100][50];
bool flag[100];
int ans = -1;

int main() {
	cin >> N;
	for (int i = 0; i < N; i++)flag[i] = true;
	for (int i = 0; i < N; i++) {
		for (int j = 0; j < N; j++) {
			cin >> greeting[i][j];
			if (i != j) {
				for (int k = 0; k < 8; k++) {
					if (greeting[i][j][k] != nyanpass[k]) {
						flag[j] = false;
						break;
					}
				}
				if (greeting[i][j][8] != NULL)flag[j] = false;
			}
		}
	}
	for (int i = 0; i < N; i++) {
		if (flag[i]) {
			if (ans == -1) {
				ans = i+1;
			}
			else {
				cout << "-1\n";
				return 0;
			}
		}
	}
		cout << ans << "\n";
	return 0;

}