#include <bits/stdc++.h>
using namespace std;
mt19937 randGenerator(1234);
long long n, k, a, b;
vector<long long> v;
void input() {
  cin >> n >> k >> a >> b;
  for (int i = 0; i < k; ++i) {
    long long x;
    cin >> x;
    v.push_back(x);
  }
  sort(v.begin(), v.end());
}
long long rec(long long l, long long r) {
  long long x = lower_bound(v.begin(), v.end(), l) - v.begin();
  long long y = upper_bound(v.begin(), v.end(), r) - v.begin();
  --y;
  long long cnt = y - x + 1;
  long long pwr;
  if (!cnt)
    pwr = a;
  else
    pwr = cnt * b * (r - l + 1);
  if (l == r || !cnt) return pwr;
  long long mid = (l + r) / 2;
  long long ans = min(pwr, rec(l, mid) + rec(mid + 1, r));
  return ans;
}
void solve() { cout << rec(1, 1LL << n) << '\n'; }
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  input();
  solve();
  return 0;
}
