#include<bits/stdc++.h>
#define IOS ios_base::sync_with_stdio(false);cin.tie();cout.tie();
using namespace std;
void solve () {
int a[1001];
int s[1001];
int r = 0;
int n; cin >> n;
for (int i = 0; i < n; i++) cin >> a[i];
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= n; j++) s[j] = 0;
s[a[0]] = 1;
int j; for (j = 1; j < n; j++) {
int k = j + (j >= i ? 1 : 0);
if (!s[k] && a[j] != k) break;
s[a[j]] = 1;
}
if (j == n) r = (r ? -1 : i);
}
cout << max(r, 0) << '\n';
}
int main() {IOS int t; cin >> t; while (t--) solve(); return 0;}
