#include "bits/stdc++.h"
#include<unordered_map>
#include<unordered_set>
#include<string>
#include<iomanip>
#include<iostream>
#include<functional>
#include<math.h>
#include<assert.h>
#include<vector>
#include<map>
#include<set>
#include<queue>
#include<string>
#pragma warning(disable:4996)

using namespace std;
using ld=long double;
const ld eps=1e-9;

#define WHATS(var)cout<<__LINE__<<' '<<#var<<"="<<var<<endl;

template<class S, class T> ostream& operator <<(ostream &os, const pair<S, T> v){
  os << "( " << v.first << ", " << v.second << ")"; return os;
}
template<class T> ostream& operator <<(ostream &os, const vector<T> &v){
  for(int i = 0; i < v.size(); i++){if(i > 0){os << " ";} os << v[i];} return os;
}
template<class T> ostream& operator <<(ostream &os, const vector<vector<T>> &v){
  for(int i = 0; i < v.size(); i++){if(i > 0){os << endl;} os << v[i];} return os;
}
template<class T> ostream& operator <<(ostream &os, const vector<set<T>> &v){
  for(int i = 0; i < v.size(); i++){if(i > 0){os << endl;} os << v[i];} return os;
}
template<class T> ostream& operator <<(ostream &os, const set<T> &v){
	int i=0;
  	for(auto it:v){
		if(i > 0){os << ' ';}
		os << it;
		i++;
	} 
	return os;
}
using ll = long long int;

int N;
ll A,B;
ll W;
ll solve(pair<ll,ll>p,int day){
	ll sa=day-p.second;
	return (p.first+(sa*(sa-1)/2*B-A*(sa-1)));
}
int main() {
	
	std::ios::sync_with_stdio(false);
	cin>>N>>A>>B>>W;
	vector<ll>ds(N+1);
	for(int i=0;i<N;++i)cin>>ds[i+1];
	deque<pair<ll,ll>>que;
	que.emplace_back(W,0);
	vector<ll>anss(N+1,1e18);
	anss[0]=W;
	for(int i=1;i<=N;++i){
		auto p=que.front();
		anss[i]=solve(p,i)+ds[i];

		while(que.size()>=2){
			auto p1=que.front();
			que.pop_front();
			auto p2=que.front();
			que.pop_front();
			if(solve(p1,i+1)>=solve(p2,i+1)){
				que.push_front(p2);
			}else{
				que.push_front(p2);
				que.push_front(p1);
				break;
			}
		}
		que.push_back(make_pair(anss[i],i));
		while(que.size()>=2){
			auto p1=que.back();
			que.pop_back();
			auto p2=que.back();
			que.pop_back();
			if(solve(p1,i+1)<=solve(p2,i+1)){
				que.push_back(p1);
			}else{
				que.push_back(p2);
				que.push_back(p1);
				break;
			}
		}
	}
	//WHATS(anss);

	ll answer=1e18;
	for(int i=0;i<=N;++i){
		ll nanswer=anss[i]-(N-i)*A+(N-i)*(N-i+1)/2*B;
		answer=min(answer,nanswer);
	}
	cout<<answer<<endl;
   	return 0;
}