#include <bits/stdc++.h>
using namespace std;
long long n, k, a, b;
vector<long long> pos;
long long an = 1e18;
long long dfs(long long l, long long r) {
  if (l == r) {
    auto it = lower_bound(pos.begin(), pos.end(), l);
    if (it != pos.end() && *it == l) {
      auto rit =
          (long long)(upper_bound(pos.begin(), pos.end(), r) - pos.begin());
      long long sz = rit - (long long)(it - pos.begin());
      return b * sz;
    }
    return a;
  } else {
    auto it = lower_bound(pos.begin(), pos.end(), l);
    if (it != pos.end() && *it <= r) {
      auto rit =
          (long long)(upper_bound(pos.begin(), pos.end(), r) - pos.begin());
      long long sz = rit - (long long)(it - pos.begin());
      long long an = b * sz * (r - l + 1);
      long long m = (l + r) >> 1;
      return min(an, dfs(l, m) + dfs(m + 1, r));
    } else {
      return a;
    }
  }
}
int32_t main() {
  ios_base::sync_with_stdio(false);
  cin >> n >> k >> a >> b;
  pos.resize(k);
  for (long long i = 0; i < k; i++) {
    cin >> pos[i];
    --pos[i];
  }
  sort(pos.begin(), pos.end());
  cout << dfs(0, (1 << n) - 1);
  return 0;
}
