#include <bits/stdc++.h>
using namespace std;
void solve() {
  int n, w;
  cin >> n >> w;
  vector<int> a(2 * n);
  for (int i = 0; i < (2 * n); i++) cin >> a[i];
  sort(a.begin(), a.end());
  double max_X = w / (3.0 * n);
  max_X = min(max_X, double(a[0]));
  max_X = min(max_X, a[n] / 2.0);
  cout << fixed << (max_X * n) + (2.0 * max_X * n);
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  solve();
  return 0;
}
