N = int(raw_input())
renchon = []
words = []
for i in range(0, N):
	words.append(raw_input().split())
for i in range(0, N):
	flag = True
	for j in range(0, N):
		if i != j:
			if words[j][i] != 'nyanpass':
				flag = False
				break
	if flag: renchon.append(i+1)
if len(renchon) == 1: print renchon[0]
else: print -1