#include <bits/stdc++.h>
using namespace std;
long long N, K, A, B;
vector<long long> v;
long long calc(long long s, long long e) {
  long long i = lower_bound(v.begin(), v.end(), s) - v.begin();
  long long j = upper_bound(v.begin(), v.end(), e) - v.begin();
  j--;
  long long x = j - i + 1;
  long long z3;
  if (x == 0)
    return A;
  else {
    long long z = B * (e - s + 1) * x;
    if (s == e) {
      if (x == 0)
        return A;
      else {
        z3 = B * (e - s + 1) * x;
        return z3;
      }
    }
    long long mid = ((e - s) / 2) + s;
    long long z1 = calc(s, mid) + calc(mid + 1, e);
    long long z2 = (long long)min(z1, z);
    return z2;
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  ;
  long long n, k, a, b;
  cin >> n >> k >> a >> b;
  N = n;
  K = k;
  A = a;
  B = b;
  long long i;
  long long y;
  for (i = 0; i < k; i++) {
    cin >> y;
    v.push_back(y);
  }
  sort(v.begin(), v.end());
  long long x = (long long)1 << n;
  long long x1 = calc(1, x);
  cout << x1, cout << "\n";
}
