#include <bits/stdc++.h>
#include <vector>
using namespace std;

int main(){
    vector<long> a;
    int N;
    long temp;
    scanf("%d",&N);
    for(int i=0;i<2*N;i++){
        scanf("%ld",&temp);
        a.push_back(temp);
    }
    sort(a.begin(),a.end());
    long ans = 0;
    for(int i=0;i<2*N;i+=2){
        ans += a[i]*a[i+1];
    }
    printf("%ld",ans);
}