#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define fi first
#define se second
void MOUST(){
    ios_base::sync_with_stdio(0);
           cin.tie(0);
}
ll p(ll a,ll b){
    return a*b+a-b;
}
int main(){
    MOUST();

    int q;cin>>q;
    while(q--){
        ll n,k=0,p=0;cin>>n;
        ll a[n];
        for(int i=0;i<n;i++){
            cin>>a[i];
            k=max(k,a[i]);
        }
        for(int i=0;i<n;i++)
            if(a[i]==k)
                p++;
        if(p>2)
            cout<<"-1\n";
        else
            cout<<n-p+1<<"\n";
    }
}