#include <bits/stdc++.h>
using namespace std;
int wait;
const long long INF = 10000005;
const int N = 1e5 + 5;
int MAX = 10000000;
long long gcd(long long a, long long b) { return (b == 0 ? a : gcd(b, a % b)); }
long long lcm(long long a, long long b) { return ((a * b) / gcd(a, b)); }
vector<long long> arr;
long long n, k, A, B;
long long solve(long long l, long long r) {
  long long i = lower_bound(arr.begin(), arr.end(), l) - arr.begin();
  long long j = upper_bound(arr.begin(), arr.end(), r) - arr.begin();
  j--;
  long long x = j - i + 1;
  long long p;
  if (x == 0) {
    p = A;
  } else {
    p = B * x * (r - l + 1);
  }
  if (l == r || x == 0) return p;
  long long mid = (l + r) / 2;
  long long min_p = min(p, solve(l, mid) + solve(mid + 1, r));
  return min_p;
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  scanf("%d%d", &n, &k);
  scanf("%d%d", &A, &B);
  for (int i = 0; i < k; ++i) {
    long long x;
    cin >> x;
    arr.push_back(x);
  }
  sort(arr.begin(), arr.end());
  long long y = (long long)(1 << n);
  long long ans = solve(1, y);
  cout << ans << endl;
}
