CCF python 中间数

n = int(input())
list1 = list(map(int, input().split()))
for i in range(n):
    low = 0
    high = 0
    for j in range(n):
        if list1[j] > list1[i]:
            high = high + 1
        if list1[j] < list1[i]:
            low = low + 1
    if low == high:
        print(list1[i])
        exit(0)
print(-1)