#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;


int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */   
    int a , s=0;
    cin>>a;
    int b[a];
    for(int i=0;i<a;i++){
     cin>>b[i];
     s = s+i;
    }
    for(int i=0;i<a;i++){
     for(int j=0;j<i;j++){
       if(b[i]>b[j]){
           int t = b[i];
           b[i] = b[j];
           b[j] = t;
       }
     }
    }
    int r[6]  ;
    int res[4] = {b[0] ,b[1] ,b[2] ,b[3] } ;
   
    int count = 0;
    for(int i=0;i<4;i++){
     for(int j=(i+1);j<4;j++){
         r[count] =  res[i]*res[j];
         count++;
      }
    }
    int sum=0;
    for(int i=0 ;i<6;i++){
     sum += r[i];
    }
    cout<<sum;
    
    return 0;
}