#include <bits/stdc++.h>
using namespace std;
int n, w;
int v[2 * 100100];
bool f(double a) {
  double ratio = a / (3.0 * n);
  if (v[0] - ratio < -1e-9 || v[n] - 2 * ratio < -1e-9) return false;
  return true;
}
double solve() {
  double beg = 0;
  double end = w;
  double ans = -1;
  for (int i = 0; i < 1000; i++) {
    double mid = (beg + end) / 2.0;
    if (f(mid)) {
      ans = mid;
      beg = mid;
    } else {
      end = mid;
    }
  }
  return ans;
}
int main() {
  cin >> n >> w;
  for (int i = 0; i < 2 * n; i++) cin >> v[i];
  sort(v, v + 2 * n);
  printf("%.10lf\n", solve());
  return 0;
}
