1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

for _ in xrange(input()):
    n = input()
    a = map(int, raw_input().split())
    if len(set(a)) == 1:
        print -1
        continue
    m = max(a)
    a = [m] + a + [m] + [m]
    for i in range(1, n+1):
        if  a[i] == m and (a[i] > a[i-1] or a[i] > a[i+1]):
            print i
            break