#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
int main(void){
    int N;long long ans=0;
    cin >> N;
    vector<long long> A(2*N);
    for(int i=0;i<2*N;i++)cin >> A[i];
    sort(A.begin(),A.end());
    for(int i=0;i<N;i++)ans+=A[2*i]*A[2*i+1];
    cout << ans << endl;
    return 0;
}