#include<cstdio>
#include<iostream>
#include<cctype>
#define ll long long
#define gys mylove
using namespace std;
int n,a[46],sum=0,l,r;
ll dp[4501];
inline void in(int &x){
    x=0;int f=1;char t=getchar();
    while(!isdigit(t)){if(t=='-')f=-1;t=getchar();}
    while(isdigit(t)){x=x*10+t-48;t=getchar();}
    x*=f;
}
inline void dpwork(int a,int sum){
	for(int i=sum;i>=0;i--)
	  if(dp[i]!=0)
	    dp[i+a]+=dp[i];
}
inline int work(){
	dp[0]=1;
	in(n);
	for(int i=1;i<=n;i++)
	{
		in(a[i]);
		dpwork(a[i],sum);
		sum+=a[i];
	}
	in(l);in(r);
}
inline void output(){
	float ans=0,p=0;
	for(int i=l;i<=r;i++)
	  ans+=dp[i];
	for(int i=0;i<=sum;i++)
	   p+=dp[i];
	printf("%.4f",ans/p);
}
int Main(){
	freopen("conbination.in","r",stdin);
	freopen("conbination.out","w",stdout);
	work();
	output();
	return 0;
}
int main(){;}
int gys=Main();