#include<iostream>
#include<cstdio>
using namespace std;
long long n,l,r,sum=0;
long long a[50],b[5000];
int main(){
	freopen("conbination.in","r",stdin);
	freopen("conbination.out","w",stdout);
	cin>>n;
	b[0]=1;
	for(int i=1;i<=n;i++){
		cin>>a[i];
		for(int j=sum;j>=0;j--)
		    if(b[j]!=0)  b[j+a[i]]+=b[j];
		sum+=a[i];
	}
	cin>>l>>r;
	double x=0,y=0;
	for(int i=0;i<=sum;i++){
		if(i>=l&&i<=r)x+=b[i];
		y+=b[i];
	}
	printf("%.4f",x/y);
	fclose(stdin);
	fclose(stdout);
	return 0;
}