def main():
    N = int(input())
    greetings = [list(input().split()) for _ in range(N)]
    greetings_t = [list(elm) for elm in zip(*greetings)]

    poi = set()
    for idx, greeting in enumerate(greetings_t):
        greeting_set = set(greeting)
        greeting_set.discard("-")
        greeting_set.discard("nyanpass")
        if not greeting_set:
            poi.add(idx)

    if len(poi) != 1:
        print(-1)
        return

    print(poi.pop()+1)


if __name__ == "__main__":
    main()