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() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long int t;
  cin >> t;
  while (t--) {
    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 max = a[0];
    long long int index = 0;
    int flag = 0;
    long long int size;
    for (long long int i = 1; i < n; i++) {
      size = a[i];
      if (i != 0 && a[i] > a[i - 1]) {
        size++;
      }
      if (i != n - 1 && a[i] > a[i + 1]) {
        size++;
      }
      if (size > max) {
        max = a[i] + i;
        index = i;
        flag = 0;
      } else if (a[i] < max) {
        max += 1;
        flag = 0;
      } else {
        flag = 1;
      }
    }
    if (flag == 0) {
      cout << index + 1 << '\n';
    } else {
      cout << "-1" << '\n';
    }
  }
}
