#include <bits/stdc++.h>
using namespace std;
long long n, k, a, b;
vector<long long> v;
long long rec(long long l, long long r) {
  long long i = lower_bound(v.begin(), v.end(), l) - v.begin();
  long long j = upper_bound(v.begin(), v.end(), r) - v.begin();
  j--;
  long long na = j - i + 1;
  long long val1 = b * (r - l + 1) * na;
  if (na == 0) return a;
  if (l == r) {
    if (na == 0)
      return a;
    else
      return val1;
  }
  long long mid = (r + l) / 2;
  long long val2 = rec(l, mid) + rec(mid + 1, r);
  long long ans = min(val1, val2);
  return ans;
}
int main() {
  cin >> n >> k >> a >> b;
  long long x;
  for (long long i = 0; i < k; i++) {
    cin >> x;
    v.push_back(x);
  }
  sort(v.begin(), v.end());
  long long l = 1, r = pow(2, n);
  long long ans = rec(l, r);
  cout << ans << endl;
}
