#include <bits/stdc++.h>
using namespace std;
const long long base = 1E9 + 7;
const int N = 100000 + 10;
const double ep = 0.0000000000001;
long long n, k, A, B;
int a[N];
int findVal(int o) {
  int i = 1;
  int j = k;
  while (i <= j) {
    int mid = (i + j) / 2;
    if (a[mid] >= o && (mid == 1 || a[mid - 1] < o)) return mid;
    if (a[mid] >= o && a[mid - 1] >= o) j = mid - 1;
    if (a[mid] < o) i = mid + 1;
  }
  return k + 1;
}
long long destroy(long long i, long long j) {
  long long u = findVal(i);
  long long v = findVal(j + 1);
  if (u == v) return A;
  long long res = (long long)(v - u) * B * (j + 1 - i);
  if (i < j && u != v) {
    int mid = (i + j) / 2;
    res = min(res, destroy(i, mid) + destroy(mid + 1, j));
  }
  return res;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin >> n >> k >> A >> B;
  for (int i = 1; i <= k; i++) cin >> a[i];
  sort(a + 1, a + k + 1);
  cout << destroy(1, pow(2, n));
  return 0;
}
