/* -*- coding: utf-8 -*-
 *
 * 1071.cc:  No.1071 ベホマラー - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 100000;
const long long LINF = 1LL << 62;

/* typedef */

typedef long long ll;

/* global variables */

int cs[MAX_N];

/* subroutines */

/* main */

int main() {
  int n, k, x, y;
  scanf("%d%d%d%d", &n, &k, &x, &y);

  for (int i = 0; i < n; i++) {
    int ai;
    scanf("%d", &ai);
    cs[i] = ((ai - 1) + (k - 1)) / k;
  }
  sort(cs, cs + n);

  ll sum = 0;
  for (int i = 0, pc = 0; i < n; i++) {
    if (y < (ll)(n - i) * x)
      sum += (ll)(cs[i] - pc) * y;
    else
      sum += (ll)(cs[i] - pc) * (n - i) * x;
    pc = cs[i];
  }

  printf("%lld\n", sum);
  return 0;
}