#include<bits/stdc++.h>
#define int long long
using namespace std;
signed main(){
    int N; cin>>N;
    vector<int> A(2*N);
    for(int i=0;i<2*N;i++)cin>>A[i];
    sort(A.begin(),A.end());
    int ans=0;
    for(int i=0;i<2*N;i+=2)ans+=A[i]*A[i+1];
    cout<<ans<<endl;
}