#include <bits/stdc++.h>
using namespace std;
template <typename T1, typename T2>
istream &operator>>(istream &istream, pair<T1, T2> &p) {
  istream >> p.first >> p.second;
  return istream;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &ostream, const pair<T1, T2> &p) {
  ostream << p.first << " " << p.second;
  return ostream;
}
template <typename T>
istream &operator>>(istream &istream, vector<T> &v) {
  for (auto &it : v) cin >> it;
  return istream;
}
template <typename T>
ostream &operator<<(ostream &ostream, const vector<T> &c) {
  for (auto &it : c) cout << it << " ";
  return ostream;
}
template <typename T>
T MIN(T first) {
  return first;
}
template <typename T, typename... Args>
T MIN(T first, Args... args) {
  return min(first, MIN(args...));
}
template <typename T>
T MAX(T first) {
  return first;
}
template <typename T, typename... Args>
T MAX(T first, Args... args) {
  return max(first, MAX(args...));
}
vector<vector<int> > adj;
vector<long long int> k;
long long int n;
long long int A, B;
long long int fnx(long long int i, long long int j) {
  long long int l = lower_bound(k.begin(), k.end(), i) - k.begin();
  long long int r = upper_bound(k.begin(), k.end(), j) - k.begin();
  return r - l;
}
long long int recursion(long long int i, long long int j) {
  if (j < i) return 0;
  long long int count_in_segment;
  count_in_segment = fnx(i, j);
  long long int val;
  if (!count_in_segment)
    val = A;
  else
    val = B * count_in_segment * (j - i + 1);
  if (i == j || count_in_segment == 0) {
    return val;
  }
  long long int mid = (j + i) / 2;
  return min(val, recursion(i, mid) + recursion(mid + 1, j));
}
void solve(long long int input) {
  long long int z;
  long long int x;
  cin >> n >> z >> A >> B;
  for (long long int i = 0; i < z; i++) {
    cin >> x;
    k.push_back(x);
  }
  sort(k.begin(), k.end());
  long long int ans = recursion(1, (1 << n));
  cout << ans << "\n";
}
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long int x = 1;
  for (long long int i = 1; i <= x; i++) solve(i);
  return 0;
}
