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 ' '*int(input()):
    n = int(input())
    a = list(map(int, input().split()))
    c = 0
    for x, y, i in zip(a, a[1:], range(1,n)):
        if y < x and c == 0: c = x; ans = i
        if c > y: c += 1
    if len(set(a)) == 1: print(-1)
    elif c == 0: print(n)
    else: print(ans)