import java.util.*;
class tournament
{
public static void main
(String args
[]) {
Scanner sc
=new Scanner
(System.
in); int n=sc.nextInt();
int team[]=new int[n];
for(int i=0;i<n;i++)
{team[i]=sc.nextInt();}
int rev=0,k=n-1;
for(int i=n-1;i>=0;i--)
{
rev=rev+(team[i]*k);
k-=2;
}
}
}
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