# -*- coding:utf-8 -*-

if __name__ == "__main__":
	n = input()
	greed = []
	ren_num = 0
	kouho = [i for i in xrange(n)]
	for i in xrange(n):
		greed.append(raw_input().split())
		for j in kouho:
			if greed[i][j] != "nyanpass" and i != j:
				kouho.remove(j)
	if len(kouho) != 1:
		print -1
	else:
		print kouho[0]+1