#include <bits/stdc++.h>
using namespace std;
long long a[200005];
int main() {
  long long n, w, i, lmt;
  cin >> n >> w;
  lmt = 2 * n;
  for (i = 1; i <= lmt; i++) scanf("%I64d", &a[i]);
  sort(a + 1, a + lmt + 1);
  float x, b, g;
  x = w / (3 * n * 1.0);
  b = a[n + 1];
  g = a[1];
  if (x <= g) {
    if (2 * x <= b) {
      g = x;
      b = 2 * x;
    } else {
      g = b / 2;
    }
  } else {
    g = a[1];
    if (2 * g <= b) {
      b = 2 * g;
    } else {
      g = b / 2;
    }
  }
  float ans = n * g + n * b;
  printf("%.8f", ans);
}
