#include<bits/stdc++.h>
using namespace std;
int main(){
    int n;cin>>n;
    while(n--){
        int a;cin>>a;
        int sha[a];
        for (int i = 0; i < a; i++) {
            /* code */
            cin>>sha[i];
        }
        sort(sha,sha+a);
        int cnt=1;
        for (int i = a-1; i >0 ; i--) {
            /* code */
            if(sha[i]==sha[i-1])cnt++;
            else break;
        }
        if(cnt>2){
            cout<<-1<<endl;
        }
        else if(cnt==2)cout<<a-1<<endl;
        else cout<<a<<endl;
    }
}