#include #include using namespace std; using ll = long long; #define int ll #define rng(i, a, b) for (int i = int(a); i < int(b); i++) #define rep(i, b) rng(i, 0, b) #define ALL(a) (a).begin(), (a).end() template void chmax(t& a, u b) { if (a < b) a = b; } template void chmin(t& a, u b) { if (b < a) a = b; } template using vc = vector; template using vvc = vc>; using pi = pair; using vi = vc; using uint = unsigned; using ull = unsigned long long; int popcount(signed t) { return __builtin_popcount(t); } int popcount(ll t) { return __builtin_popcountll(t); } bool ispow2(int i) { return i && (i & -i) == i; } ll mask(int i) { return (ll(1) << i) - 1; } int lcm(int a, int b) { return a / __gcd(a, b) * b; } signed main() { cin.tie(0); ios::sync_with_stdio(0); cout << fixed << setprecision(20); int n; cin >> n; vc a(2 * n); rep(i, n * 2) cin >> a[i]; sort(ALL(a), greater()); int ans = 0; rep(i, n) { ans += a[2 * i] * a[2 * i + 1]; } cout << ans << endl; }