#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
#define REP(i,n) for(int i=0,_n=(int)(n);i<_n;++i)
#define ALL(v) (v).begin(),(v).end()
#define CLR(t,v) memset(t,(v),sizeof(t))
template<class T1,class T2>ostream& operator<<(ostream& os,const pair<T1,T2>&a){return os<<"("<<a.first<<","<<a.second<< ")";}
template<class T>void pv(T a,T b){for(T i=a;i!=b;++i)cout<<(*i)<<" ";cout<<endl;}
template<class T>void chmin(T&a,const T&b){if(a>b)a=b;}
template<class T>void chmax(T&a,const T&b){if(a<b)a=b;}

ll nextLong() { ll x; scanf("%lld", &x); return x;}

int main2() {
  int N = nextLong();
  int K = nextLong();
  ll X = nextLong();
  ll Y = nextLong();

  vector<ll> A(N);
  vector<ll> S(N+1);
  REP(i, N) {
    A[i] = nextLong();
    A[i] = (A[i] - 1 + K - 1) / K;
  }
  sort(ALL(A));
  S[N] = 0;
  for (int i = N - 1; i >= 0; i--) S[i] = S[i+1] + A[i];

  ll ans = S[0] * X;
  for (int i = 0; i < N; i++) {
    ll val = A[i] * Y + (S[i] - (N-i)*A[i]) * X;
    chmin(ans, val);
  }
  cout << ans << endl;
  return 0;
}

int main() {

#ifdef LOCAL
  for (;!cin.eof();cin>>ws)
#endif
    main2();
  return 0;
}