#include <bits/stdc++.h>
using namespace std;
long long read() {
  long long f = 1, x = 0;
  char c = getchar();
  while (c < '0' || '9' < c) {
    if (c == '-') f = -1;
    c = getchar();
  }
  while ('0' <= c && c <= '9') x = (x << 3) + (x << 1) + c - '0', c = getchar();
  x *= f;
  return x;
}
int n, k;
long long a[100000 + 5], A, B;
long long DFS(long long l, long long r, int L, int R) {
  if (R < L) return A;
  if (l == r) return B * (R - L + 1);
  long long mid = (l + r) >> 1;
  int p = lower_bound(a + 1, a + k + 1, mid + 1) - (a + 1);
  long long tmp = min(B * (R - L + 1) * (r - l + 1),
                      DFS(l, mid, L, p) + DFS(mid + 1, r, p + 1, R));
  return tmp;
}
int main() {
  n = read(), k = read();
  A = read(), B = read();
  for (int i = 1; i <= k; i++) a[i] = read();
  sort(a + 1, a + k + 1);
  printf("%lld\n", DFS(1, 1ll << n, 1, k));
  return 0;
}
