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;
int32_t main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  long long t;
  cin >> t;
  while (t--) {
    long long n, ans = 0, f = 0;
    bool fa, fb;
    cin >> n;
    long long a[n];
    for (long long i = 0; i < n; i++) cin >> a[i];
    for (long long i = 0; i < n - 1; i++) {
      if (a[i] != a[i + 1]) {
        f++;
        break;
      }
    }
    long long mx = a[0];
    for (long long i = 1; i < n; i++) {
      mx = max(mx, a[i]);
    }
    if (f == 0)
      ans = -1;
    else {
      for (long long i = 0; i < n - 1; i++) {
        if ((a[i] == mx) && (a[i] != a[i + 1])) {
          ans = i + 1;
          break;
        } else if ((a[i + 1] == mx) && (a[i] != a[i + 1])) {
          ans = i + 2;
          break;
        }
      }
    }
    cout << ans << endl;
  }
}
