#include <bits/stdc++.h>

#define For(i, a, b) for (int i = (int)(a); i < (int)(b); ++i)
#define rFor(i, a, b) for (int i = (int)(a)-1; i >= (int)(b); --i)
#define rep(i, n) For((i), 0, (n))
#define rrep(i, n) rFor((i), (n), 0)
#define fi first
#define se second

using namespace std;

typedef long long lint;
typedef unsigned long long ulint;
typedef pair<int, int> pii;
typedef pair<lint, lint> pll;

template <class T>
bool chmax(T &a, const T &b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}
template <class T>
bool chmin(T &a, const T &b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}

template <class T>
T div_floor(T a, T b) {
    if (b < 0) a *= -1, b *= -1;
    return a >= 0 ? a / b : (a + 1) / b - 1;
}
template <class T>
T div_ceil(T a, T b) {
    if (b < 0) a *= -1, b *= -1;
    return a > 0 ? (a - 1) / b + 1 : a / b;
}

template <typename T>
struct coord_comp {
    vector<T> v;
    bool sorted = false;

    coord_comp() {}

    int size() { return v.size(); }

    void add(T x) { v.push_back(x); }

    void build() {
        sort(v.begin(), v.end());
        v.erase(unique(v.begin(), v.end()), v.end());
        sorted = true;
    }

    int get_idx(T x) {
        assert(sorted);
        return lower_bound(v.begin(), v.end(), x) - v.begin();
    }

    T &operator[](int i) { return v[i]; }
};

constexpr lint mod = 1000000007;
constexpr lint INF = mod * mod;
constexpr int MAX = 100010;

int main() {
    int n;
    scanf("%d", &n);
    lint a[n * 2];
    rep(i, n * 2) scanf("%lld", &a[i]);
    sort(a, a + n * 2);

    lint ans = 0;
    rep(i, n) ans += a[i * 2] * a[i * 2 + 1];
    printf("%lld\n", ans);
}