def main():
    N = int(input())
    A = [input().split() for _ in range(N)]
    renge = []
    for i in range(N):
        for j in range(N):
            if i != j and A[j][i] != 'nyanpass':
                break
        else:
            renge.append(i)
    if len(renge) == 1:
        print(renge[0] + 1)
    else:
        print(-1)
    
    
if __name__ == '__main__':
    main()