题解 | 预知

while True:
    try:
        T = int(input())
        for _ in range(T):
            n = int(input())
            a = list(map(int, input().split()))
            if n == 1:      # 只有一种牌
                print(-1)
            elif a.count(1) == len(a):  # 每种牌都只有1张
                print(0)
            elif a.count(1) == len(a) - 1:  # 只有1种牌大于1张
                print(max(a) - 1)
            else:
                print(max(a))
    except:
        break