#include <iostream>
#include <math.h>
 
int t, k, n;
long long suma;
double srednia;
 
using namespace std;
 
int main()
{
    cin>>t;
    while(t--)
    {
        cin>>n;
        int a[n];
        long long int iloczyn[n];
        for (int i=0; i<n; i++)
        {
            cin>>a[i];
            iloczyn[i]=1;
        }
        k=0;
        srednia=0;
        while (srednia<4)
        {
            k++;
            suma=0;
            for (int i=0; i<n; i++)
            {
            iloczyn[i]*=a[i];
            suma+=iloczyn[i];
            }
            srednia=pow(suma/n, 1.0/k);
            if (k==32) {k=-1; break;}
        }
        cout<<k<<endl;
    }
    return 0;
}

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

NAo1CjEgMiAzIDEgMwo0CjEgMiAzIDUKNQoxIDEgNSAxIDEKMgo0IDI=

4
5
1 2 3 1 3
4
1 2 3 5
5
1 1 5 1 1
2
4 2