#include<cstdio>
int n,sum=0,l,r;
double ansa=0.000,ansb=0.000;
long long ans[4501];
int main()
{
	freopen("conbination.in","r",stdin);
	freopen("conbination.out","w",stdout);
	ans[0]=1;
	scanf("%d",&n);
	for(int i=1,a;i<=n;i++)
	{
		scanf("%d",&a);
		for(int j=sum;j>=0;j--)
			if(ans[j]!=0)
	    		ans[j+a]+=ans[j];
		sum+=a;
	}
	scanf("%d%d",&l,&r);
	for(int i=l;i<=r;i++)
		ansa+=ans[i];
	for(int i=0;i<=sum;i++)
		ansb+=ans[i];
	printf("%.4lf",ansa/ansb);
	return 0;
}