N = int(raw_input())
A = [raw_input().split() for i in range(N)]
number = []
for j in range(N):
	if A[0][j] == 'nyanpass' or j == 0:
		f = False
		for i in range(N):
			if i == j:continue
			if A[i][j] != 'nyanpass':
				f = True
				break
		if not f:number.append(j + 1)
print -1 if len(number) != 1 else number[0]