N = int(raw_input())
notrenchon = []
for i in xrange(N):
    A = raw_input().split()
    for j in xrange(N):
        if A[j] not in ('nyanpass', '-'):
            notrenchon.append(j + 1)

candset = set([i for i in xrange(1, N+1)]) - set(notrenchon)
if len(candset) == 1:
    print candset.pop()
else:
    print -1