#include <iostream>

using namespace std;

int t,n,a[200000],ans[10000];

int main()
{
    cin >> t;
    int max = a[0];
    for (int i = 0; i < t; i++){
        cin >> n;
        int temp = 0;
        int newn = n;
        for (int j = 0; j < n; j++){
            cin >> a[j];
        }
        for(int j = 0; j < n-1; j++){
            temp = 0;
            for (int k = j+1; k < n; k++){
                if(a[j] == a[k]){
                    temp++;
                }
            }
            if (temp >= 2){
                ans[i] = -1;
                break;
            }
            else {
                newn -= temp;
            }
        }
        if(ans[i] != -1){
            ans[i] = newn;
        }
        
    }
    
    for(int i = 0; i < t; i++){
        cout << ans[i] << "\n";
    }
    return 0;
}