villager = []
nyanpass = -1

n = int(input())

for i in range(n):
    villager.append(input().split())

for j in range(n):
    for i in range(n):
        if i != j and villager[i][j] != 'nyanpass':
            break
    else:
        if nyanpass == -1:
            nyanpass = j + 1
        else:
            print('-1')
            break
else:
    print(nyanpass)