N = int(input())
A = [input().split() for _ in range(N)]
S = "nyanpass"

s = set()
for j in range(N):
    flag = True
    for i in range(N):
        if i == j:continue
        if A[i][j] != S:
            flag = False
            break
    if flag:
        s.add(j)
if len(s) == 1:
    for v in s:
        print(v+1)
else:
    print(-1)