#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <vector>
#include <list>
#include <queue>
#include <map>
#include <set>
#include <utility>
#include <string>
#include <cstring>
#include <sstream>
#include <cmath>
#include <limits>
#include <algorithm>
#include <iterator>
#include <memory.h>
#include <time.h>

using namespace std;

#define CUR_NAMESPACE namespace conbination {
CUR_NAMESPACE

const int N = 50;
const int C = 4505;
typedef unsigned long long ULL;

class Solver
{
private:
	int n;
	int arr[N];
	ULL dp[C];
public:
	void Solve()
	{
		scanf("%d", &n);
		int c = 0;
		for (int i = 1; i <= n; i++) {
			scanf("%d", &arr[i]);
			c += arr[i];
		}
		for (int i = 0; i <= n; i++) dp[0] = 1;
		dp[arr[1]] = 1;
		for (int i = 2; i <= n; i++) {
			for (int j = c; j >= arr[i]; j--) {
				dp[j] += dp[j - arr[i]];
			}
		}
		double denom = 0.0;
		for (int i = 0; i <= c; i++) {
			denom += dp[i];
		}
		int l, r;
		scanf("%d%d", &l, &r);
		double nom = 0.0;
		for (int i = l; i <= r; i++) {
			nom += dp[i];
		}
		printf("%.4f", nom / denom);
	}
} solver;

void Launch()
{
	solver.Solve();
}

#define NAMESPACE_END }
NAMESPACE_END

int main()
{
    freopen("conbination.in", "r", stdin);
	freopen("conbination.out", "w+", stdout);
	conbination::Launch();
	return 0;
}