#include<bits/stdc++.h>
#define il inline
#define ll long long
#define lb long double
using namespace std;
il ll read(){
	ll a=0,f=1;
	char ch=getchar();
	while(ch<'0'||ch>'9'){if(ch=='-')f=-f;ch=getchar();}
	while(ch>='0'&&ch<='9'){a=a*10+ch-'0';ch=getchar();}
	return a*f;
}
ll n,A,B,f[300010],ruby[300010],ans=1e18,q[300010],head,tail;
ll Y(ll x){
	return f[x]+A*x+(x+1)*x/2*B;
}
lb K(ll x,ll y){
	return (lb)1.0*(Y(x)-Y(y))/(x-y);
}
int main(){
//	freopen("chips.in","r",stdin);
//	freopen("chips.out","w",stdout);
	memset(f,0x3f,sizeof f);
	n=read();A=read();B=read();f[0]=read();
	q[1]=0;head=1;tail=1;
	for(int i=1;i<=n;++i){
		ruby[i]=read();
		while(head<tail&&K(q[head],q[head+1])<=i*B)++head;
		f[i]=min(f[i],f[q[head]]+ruby[i]-A*(i-q[head]-1)+(i-q[head])*(i-q[head]-1)*B/2);
		while(head<tail&&K(q[tail],i)<=K(q[tail-1],q[tail]))--tail;
		q[++tail]=i;
	}
	for(int i=0;i<=n;++i)
		ans=min(ans,f[i]-A*(n-i)+(n-i+1)*(n-i)*B/2);
	cout<<ans;
	return 0;
}