Problem: You have a circle of length C, and you are placing N arcs on it. Arc i has length L_i.

Every arc i is placed on the circle uniformly at random: a random real point on the circle is chosen, then an arc of length L_i centered at this point appears.

Note that the arcs are placed independently. For example, they may intersect or contain each other.

What is the probability that every real point of the circle will be covered by at least one arc? Assume that an arc covers its ends.

Constraints

* 2 \leq N \leq 6
* 2 \leq C \leq 50
* 1 \leq L_i < C
* All input values are integers.

Input

Input is given from Standard Input in the following format:


N C
L_1 L_2 ... L_N


Output

Print the probability that every real point of the circle will be covered by at least one arc. Your answer will be considered correct if its absolute error doesn't exceed 10^{-11}.

Examples

Input

2 3
2 2


Output

0.3333333333333333


Input

4 10
1 2 3 4


Output

0.0000000000000000


Input

4 2
1 1 1 1


Output

0.5000000000000000


Input

3 5
2 2 4


Output

0.4000000000000000


Input

4 6
4 1 3 2


Output

0.3148148148148148


Input

6 49
22 13 27 8 2 19


Output

0.2832340720702695

Solution (in CPP):

Solution:
#include <algorithm>  
#include <iostream>  
#include <sstream>  
#include <string>  
#include <cstring>
#include <vector>  
#include <queue>  
#include <set>  
#include <map>  
#include <cstdio>  
#include <cstdlib>  
#include <cctype>  
#include <cmath>  
#include <list>  
#include <cassert>
#include <ctime>
#include <climits>
using namespace std;  

#define PB push_back  
#define MP make_pair  
#define SZ(v) ((int)(v).size())  
#define FOR(i,a,b) for(int i=(a);i<(b);++i)  
#define REP(i,n) FOR(i,0,n)  
#define FORE(i,a,b) for(int i=(a);i<=(b);++i)  
#define REPE(i,n) FORE(i,0,n)  
#define FORSZ(i,a,v) FOR(i,a,SZ(v))  
#define REPSZ(i,v) REP(i,SZ(v))  
typedef long long ll;
typedef unsigned long long ull;
ll gcd(ll a,ll b) { return b==0?a:gcd(b,a%b); }

const int MAXN = 6;
const int MAXCLEN = 50;
const int MAXP = MAXN*MAXCLEN;

int n, clen;
int alen[MAXN];
int p[MAXN]; // relative order of fractions
int r[MAXN];

//dp[i][mask][j] is number of ways that we cover exactly the first j segments with arcs when the only the arcs in mask start on the first i points (conditional on relative order of fractions)
double dp[MAXP + 1][1 << (MAXN - 1)][MAXP + 1];

double solve() {
	REP(i, n) r[p[i]] = i;
	memset(dp, 0, sizeof(dp));
	dp[1][0][n*alen[n - 1]] = 1;
	FOR(i, 1, n*clen) REP(mask, 1 << (n - 1)) FORE(j, 1, n*clen) if (dp[i][mask][j] != 0) {
		//no arcs starts at point i+1
		dp[i + 1][mask][j] += dp[i][mask][j];
		//arc r[i%n] starts at point i+1
		int idx = r[i%n];
		if (idx != n - 1 && (mask&(1 << idx)) == 0) {
			int nj = j < i ? j : max(j, min(n*clen, i + n*alen[idx] - 1));
			dp[i + 1][mask | (1 << idx)][nj] += dp[i][mask][j];
		}
	}
	//FORE(i, 1, n*clen) REP(mask, 1 << (n - 1)) FORE(j, 1, n*clen) if (dp[i][mask][j] != 0) printf("%d,%x,%d = %lf\n", i, mask, j, dp[i][mask][j]);
	double num = dp[n*clen][(1 << (n - 1)) - 1][n*clen], den = 1; REP(i, n - 1) den *= clen; double ret = num / den;
	//printf("p:"); REP(i, n) printf(" %d", p[i]); printf(" -> %lf (%lf/%lf)\n", ret,num,den);
	return ret;
}

void run() {
	scanf("%d%d", &n, &clen); REP(i, n) scanf("%d", &alen[i]);
	sort(alen, alen + n);
	REP(i, n - 1) p[i] = i + 1; p[n - 1] = 0;
	double ret = 0; int nperm = 0;
	do {
		ret += solve(); ++nperm;
	} while (next_permutation(p, p + n - 1));
	printf("%.15lf\n", ret / nperm);
}

int main() {
	run();
	return 0;
}