#code
def find_element(a,size):
    max_ele,min_ele = ['None'] * size, ['None'] * size 
    max_ele[0] = a[0]
    min_ele[size - 1] = a[size - 1]
    flag = 0
    for i in range(1,size):
        max_ele[i] = max(max_ele[i-1],a[i])
        min_ele[size - i - 1] = min(min_ele[size - i],a[size - i - 1])
    for i in range(1,size-1):
        if max_ele[i] == min_ele[i]:
            flag = 1
            print(max_ele[i])
            break
    if flag == 0:
        print(-1)
        
t = int(input())
for i in range(t):
    n = int(input())
    s = input()
    arr = list(map(int,s.split()))
    find_element(arr,len(arr))