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

# cook your dish here
for _ in range(int(input())):
        n=int(input())
        a=list(map(int,input().split()))
        if(len(list(set(a)))==1):
                print(-1)
                continue
        v=a[0]
        p=-1
        for i in range(1,n):
                if(a[i]<v):
                     
                        p=i-1
                        break;
                v=a[i]
        if(p+1==0):
                print(n-1)
                continue
        print(p+1)