#include <stdlib.h>
#include <stdio.h>
#include <string.h>

#define UREP(i,n) for(unsigned i = 0; i < (n); i++)

int main(){
	unsigned N;
	scanf("%d", &N);
	char ***A;
	A = (char ***)malloc(sizeof(char **) * N);
	UREP(i, N){
		A[i] = (char **)malloc(sizeof(char *) * N);
		UREP(j, N){
			A[i][j] = (char *)malloc(32);
			scanf("%s", A[i][j]);
		}
	}
	unsigned ren, count = 0, all;
	UREP(i, N){
		all = 1;
		UREP(j, N){
			if(i != j && strcmp(A[j][i], "nyanpass")) all = 0;
		}
		if(all){
			ren = i;
			count++;
		}
	}
	if(count == 1) printf("%d\n", ren + 1);
	else printf("-1\n");
}