//TLE
#include <iostream>
#include <algorithm>
#define int long long
using namespace std;

int n, a, b, w;
int d[300001];
int dp[300001];

signed main() {
	int i, j;
	
	cin >> n >> a >> b >> w;
	for (i = 0; i < n; i++) cin >> d[i];
	
	//断食スタートの場合を考慮すべし
	for (i = 0; i < n + 1; i++) {
		dp[i] = w + b * i * (i + 1) / 2 - a * i;
	}
	
	dp[0] = w;
	for (i = 0; i < n; i++) {
		for (j = i + 1; j < n + 1; j++) {
			//(i..j)で断食
			int day = j - i - 1;
			int stress = b * (day + 1) * day / 2;
			dp[j] = min(dp[j], dp[i] + d[i] + stress - a * day);
		}
	}
	cout << dp[n] << endl;
	return 0;
}