#include <bits/stdc++.h>
using namespace std;
template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;}
template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;}
using Int = long long;
const char newl = '\n';

//INSERT ABOVE HERE
signed main(){
  cin.tie(0);
  ios::sync_with_stdio(0);


  Int n,k,x,y;
  cin>>n>>k>>x>>y;

  vector<Int> as(n);
  for(Int i=0;i<n;i++) cin>>as[i];

  vector<Int> bs(n);
  for(Int i=0;i<n;i++)
    bs[i]=(as[i]-1+k-1)/k;

  Int ans=1e18;
  auto calc=[&](Int t)->Int{
    Int res=t*y;
    for(Int b:bs)
      if(b>t) res+=(b-t)*x;
    chmin(ans,res);
    return res;
  };

  Int L=0,R=1e9;
  calc(L);
  calc(R);
  while(L+10<R){
    Int M1=(L+R)>>1;
    Int M2=M1+1;
    if(calc(M1)>calc(M2)) L=M1;
    else R=M2;
  }
  for(Int t=L;t<R;t++) calc(t);
  cout<<ans<<endl;
  return 0;
}