Can someone explain this?

1

Ques-

Code-
#include

using namespace std;

int main(){

int n,x,sum=0; 

cin>>n;

for(int i=0;i<n;i++){   

    cin>>x;

    sum+=x*i;

}

cout<<sum*4<<"\n";

return 0;

}

Why are we multiplying sum by 4 ?