#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cstring>
int n,a[46],sum=0,l,r;
long long ans[4501];
void hua_ji(int a,int sum)
{
	for(int i=sum;i>=0;i--)
	  if(ans[i]!=0)
	    ans[i+a]+=ans[i];
}
int main()
{
	freopen("conbination.in","r",stdin);
	freopen("conbination.out","w",stdout);
	memset(ans,0,sizeof(ans));
	ans[0]=1;
	scanf("%d",&n);
	for(int i=1;i<=n;i++)
	  scanf("%d",&a[i]);
//	sort(a+1,a+(n+1));
	for(int i=1;i<=n;i++)
	{
		hua_ji(a[i],sum);
		sum+=a[i];
	}
	scanf("%d%d",&l,&r);
	float ansa=0,ansb=0;
	for(int i=l;i<=r;i++)
	  ansa+=ans[i];
	for(int i=0;i<=sum;i++)
	   ansb+=ans[i];
	printf("%.4f",ansa/ansb);
	return 0;
}