#include <iostream>
#include <math.h>
using namespace std;
double root(double x, double k)
{
double wynik;
wynik=exp((log(x))/k);
return wynik;
}
int main()
{
unsigned int t;
cin >> t;
while(t--)
{
int n;
cin >> n;
double *tab=new double[n];
for(unsigned short i=0;i<n;i++)
{
cin >> tab[i];
}
unsigned int pot;
double k=0.00, hist=-1.00;
while(true)
{
double tmp, x;
for(unsigned short i=0;i<n;i++)
{
tmp+=((pow(tab[i],k))/n);
}
x=root(tmp,k);
if(x>=4.00){pot=k; break;}
else if(x==hist){pot=(-1); break;}
hist=x;
k++;
}
cout << pot << "\n";
delete [] tab;
tab=0;
}
}
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