#include <bits/stdc++.h>
using namespace std;
const int N = 200000;
int a[N];
void solve() {
  cout.precision(17);
  int n, w;
  cin >> n >> w;
  for (int i = 0; i < 2 * n; i++) {
    cin >> a[i];
  }
  sort(a, a + 2 * n);
  long double girls = min({w / (3.0 * n), a[0] * 1.0, a[n] / 2.0});
  cout << n * girls + n * girls * 2;
}
int main() {
  solve();
  getchar();
  getchar();
}
