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

typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef long long LL;
typedef pair<LL, LL> PLL;

#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define EB emplace_back
#define MP make_pair
#define SZ(a) int((a).size())
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())

#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)

#define FF first
#define SS second
template<class S, class T>
istream& operator>>(istream& is, pair<S,T>& p){
  return is >> p.FF >> p.SS;
}

const double EPS = 1e-10;
const double PI  = acos(-1.0);
const LL MOD = 1e9+7;

const int MAX = 300010;
LL N, A, B, W;
LL dp[MAX];
LL xs[MAX];
LL f(LL x){
  return -x*A + x*(x+1)/2 * B;
}
int main(){
  cin.tie(0);
  ios_base::sync_with_stdio(false);

  cin >> N >> A >> B >> W;
  REP(i,N) cin >> xs[i];

  fill(dp, dp+MAX, 1e15);
  int R = N;
  dp[N] = W;
  for(int i=N-1;i>=0;--i){
	for(int j=R;j>=i+1;--j){
	  LL nxt = xs[i]+f(j-i-1)+dp[j];
	  if(nxt < dp[i]){
		dp[i] = nxt;
		R = j;
	  }
	}
  }

  LL ans = 1e15;
  REP(i,N+1) ans = min(ans, f(i)+dp[i]);
  cout << ans << endl;

  return 0;
}