#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
#else
  #define Debug(...) void(0)
#endif
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

int main() {
  int n;
  cin >> n;
  vector<ll> a(n * 2);
  rep(i, 2 * n) cin >> a[i];
  sort(a.begin(), a.end());
  ll ans = 0;
  rep(i, n) ans += a[2 * i] * a[2 * i + 1];
  cout << ans << endl;
  return 0;
}