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

ans = []
for j in range(N):
    if all(S[i][j] == "nyanpass" for i in range(N) if i != j):
        ans.append(j + 1)

if len(ans) == 1:
    print(ans[0])
else:
    print(-1)