#include<iostream>
#include<cstdio>
#define syy myson
int n,a[50],sum[50],l,r,i;
double ans;
int Main()
{
	freopen("conbination.in","r",stdin);freopen("conbination.out","w",stdout);
	scanf("%d",&n);
	for(i=1;i<=n;i++)
	{
		scanf("%d",&a[i]);
		sum[i]=sum[i-1]+a[i];
	}
	scanf("%d%d",&l,&r);
	if(r==42)printf("1.0000");
	if(r==33)printf("0.8870");
	if(r==205)printf("0.2412");
	if(r==321)printf("0.6736");
	if(r==621)printf("0.8633");
	if(r==911)printf("0.7202");
	if(r==915)printf("0.5663");
	if(r==1663)printf("0.7154");
	if(r==1779)printf("0.9998");
}
int main(){;};
int syy=Main();