N = int(input())
flag = [1]*N
A = [input().split() for _ in range(N)]
for i in range(N):
    for j in range(N):
        if i==j:
            continue
        if A[i][j]!="nyanpass":
            flag[j] = 0
if sum(flag) != 1:
    print(-1)
else:
    print(flag.index(1)+1)