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:
//by yjz
#include<bits/stdc++.h>
using namespace std;
#define FF first
#define SS second
#define PB push_back
#define MP make_pair
#define foreach(it,s) for(__typeof((s).begin()) it=(s).begin();it!=(s).end();it++)
#ifndef LOCAL
#define cerr if(0)cout
#endif
typedef long long ll;

int N, L;
int a[7];
//mx_pos mx_lv lv_mask used_mask
double dp[2][51][7][1<<5][1<<5];
int main()
{
	cin>>N>>L;
	for (int i=0; i<N; i++) cin>>a[i];
	sort(a, a+N);
	double ans = 0;
	int p = 0;
	dp[p][a[N-1]][0][0][0] = 1;
	for (int i=0; i<L; i++)
	{
		for (int j=0; j<N-1; j++)
		{
			int np = p^1;
			memset(dp[np], 0, sizeof(dp[np]));
			for (int mxi=0; mxi<=L; mxi++)
			{
				for (int mxj=0; mxj<N; mxj++)
				{
					if (MP(i,j+1)>=MP(mxi, mxj)) continue;
					for (int lv_mask=0; lv_mask<(1<<N-1); lv_mask++)
					{
						for (int used_mask=0; used_mask<(1<<N-1); used_mask++)
						{
							double &cur = dp[p][mxi][mxj][lv_mask][used_mask];
							if (cur==0) continue;
							dp[np][mxi][mxj][lv_mask][used_mask] += cur;
							//cerr<<i<<","<<j<<" "<<mxi<<" "<<mxj<<" "<<lv_mask<<" "<<used_mask<<":"<<cur<<endl;
							if (!((lv_mask>>j)&1))
							{
								for (int x=0; x<N-1; x++)
								{
									if ((used_mask>>x)&1) continue;
									int ni = mxi, nj = mxj;
									if (MP(i+a[x], j+1)>MP(ni, nj))
									{
										ni = i+a[x];
										nj = j+1;
									}
									if (MP(ni,nj)>MP(L,0)) ni = L, nj = 0;
									dp[np][ni][nj][lv_mask|(1<<j)][used_mask|(1<<x)] += cur/L;
								}
							}
						}
					}
				}
			}
			p = np;
		}
	}
	ans += dp[p][L][0][(1<<N-1)-1][(1<<N-1)-1];
	for (int i=1; i<=N-1; i++) ans /= i;
	cout<<fixed<<setprecision(11)<<ans<<endl;
	return 0;
}