#include "bits/stdc++.h"
 
using namespace std;
typedef long long ll;

void solve() {
    int n;
    cin >> n;
    vector<int> v(n);
    map<int, int> mp;
    for (auto &x : v) {
        cin >> x;
        mp[x]++;
    }

    int mx = *max_element(v.begin(), v.end());
    if (mp[mx] > 2) {
        cout << -1 << '\n';
        return;
    }
    cout << n - mp[mx] + 1 << '\n';
}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int t = 1;
    cin >> t;
    while (t--) {
        solve();
    }
}