#include <iostream>
using namespace std;
int t,n,a[200000],ans[10000];
int main()
{
cin >> t;
int temp = 0;
for (int i = 0; i < t; i++){
cin >> n;
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;
}