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

from math import *
sInt = lambda: int(input())
mInt = lambda: map(int, input().split())
lInt = lambda: list(map(int, input().split()))

t= sInt()

for _ in range(t):
    n = sInt()
    a = lInt()
    ans = 1
    c = a.count(max(a))
    f = a.index(max(a), 0, n)
    done = 0
    if c==n:
        ans = -1
    elif f==n-1:
        ans += f
    else:
        for i in range(f,n):
            if a[i]!=max(a):
                ans += i-1
                done = 1
                break
        if done==0:
            ans = -1
    print(ans)














