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

#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int t;
  cin >> t;
  while (t--) {
    bool flag = false;
    int count = 0;
    long long int n;
    cin >> n;
    long long int a[n];
    for (long long int i = 0; i < n; i++) {
      cin >> a[i];
    }
    long long int idx = 0;
    long long int lst_idx = 0;
    for (long long int i = 0; i < n - 1; i++) {
      if (a[i] > a[i + 1]) {
        a[i + 1] = a[i] + 1;
        lst_idx = i + 1;
      } else if (a[i] == a[i + 1]) {
        count++;
        idx = idx + 1;
      } else {
        idx = idx + 1;
      }
    }
    if (count == n - 1) {
      cout << -1 << endl;
    } else {
      cout << idx + 1 << endl;
    }
  }
}
