#!/usr/bin/ruby

def is_minimam(a1,b1,a2,b2,a3,b3)
	(a2-a1)*(b3-b2)>=(b2-b1)*(a3-a2)
end
def is_maximam(a1,b1,a2,b2,a3,b3)
	is_minimam(-a1,-b1,-a2,-b2,-a3,-b3)
end
def check(l1,l2,l3)
	is_minimam(l1[0],l1[1],l2[0],l2[1],l3[0],l3[1])
end
def calc(l,now)
	l[0]*now+l[1]
end

class ConvexHullTrick
	def initialize
		@deque=100000.times.map{[0,0]}
		@s=0
		@t=0
	end
	def add(a,b)
		l=[a,b]
        while @s+1<@t&&check(@deque[@t-2],@deque[@t-1],l)
			@t-=1
		end
		@deque[@t]=l
		@t+=1
    end
	def get(now)
        while @s+1<@t&&calc(@deque[@s],now)>=calc(@deque[@s+1],now)
			@s+=1
		end
        calc(@deque[@s],now)
	end
end

n,a,b,w=gets.split.map(&:to_i)
d=gets.split.map(&:to_i)
deq=ConvexHullTrick.new
dp=[Float::INFINITY]*(n+1)
dp[0]=w

deq.add( - 0 * b,dp[0] + 0 * a + b * 0 * (0 - 1) / 2)
n.times{|i|
	dp[i + 1] = d[i] - i * a + ( b * i * (i + 1)) / 2 + deq.get(i)
	deq.add( - (i + 1) * b , dp[i + 1] + (i + 1) * a + ( b * (i + 1) * i) / 2)
}

res=Float::INFINITY
(n+1).times{|i|
	res=[res,dp[i] - a * (n -i) + b * (n - i) * (n - i + 1) / 2].min
}
p res