#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
constexpr int Inf = 2000000030;
constexpr ll INF= 2000000000000000001;
constexpr ll MOD = 1000000007;
const double PI = 3.14159265358979323846;
typedef pair<ll,ll> P;
typedef pair<ll,P> PP;

template<typename T> 
vector<T> make_vector(size_t s) {
    return vector<T>(s);
}

template<typename T,typename... Args>
auto make_vector(size_t s,Args... args) {
    return vector(s,make_vector<T>(args...));
}

template<typename T> inline bool chmax(T &a, T b) {
    if (a < b) {
        a = b;
        return 1;
    }
    return 0;
}

template<typename T> inline bool chmin(T &a, T b) {
    if (a > b) {
        a = b;
        return 1;
    }
    return 0;
}

ll mod(ll val, ll M) {
    val = val % M;
    if(val < 0) {
        val += M;
    }
    return val;
}

int main() {
    int N;
    cin >> N;
    vector<ll> vec(2 * N);
    for(int i = 0;i < 2 * N;i++) {
        cin >> vec.at(i);
    }
    sort(vec.begin(),vec.end());
    reverse(vec.begin(),vec.end());
    ll ret = 0;
    for(int i = 0;i < N;i++) {
        ret += vec.at(i * 2) * vec.at(i * 2 + 1);
    }
    cout << ret << endl;
}