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:
// I need some holiday
// But I don't wish that everyday is holiday
// Because I didn't bear the pain
// Because it wasn't a true freedom
//         ——『イヤホンと蝉時雨』·Orangestar

#include <bits/stdc++.h>

using namespace std;

typedef long long LL;
typedef long double LD;
typedef unsigned int UI;
typedef pair<int, int> pii;

#define DEBUG(...) fprintf(stderr, __VA_ARGS__)
#define MP make_pair
#define fst first
#define snd second
#define SZ(u) ((int) (u).size())
#define ALL(u) (u).begin(), (u).end()

inline void proc_status()
{
	ifstream t("/proc/self/status");
	cerr << string(istreambuf_iterator<char>(t), istreambuf_iterator<char>()) << endl;
}

template<typename T> inline int chkmin(T &a, const T &b) { return b < a ? a = b, 1 : 0; }
template<typename T> inline int chkmax(T &a, const T &b) { return b > a ? a = b, 1 : 0; }
template<typename T> inline T sqr(const T &val) { return val * val; }

namespace fastIO
{
	const int MAX_BUFFER_SIZE = 1 << 16;

	char buffer[MAX_BUFFER_SIZE], *cur = buffer, *ed = buffer;

	inline char getc() { return cur == ed && (ed = (cur = buffer) + fread(buffer, 1, MAX_BUFFER_SIZE, stdin), cur == ed) ? EOF : *cur++; }
}
using fastIO::getc;

template<typename T> inline T read()
{
	register T sum(0), fg(1);
	register char ch(getc());
	for(; !isdigit(ch); ch = getc()) if(ch == '-') fg = -1;
	for(;  isdigit(ch); ch = getc()) sum = sum * 10 - '0' + ch;
	return sum * fg;
}

inline char *read_str(char *s)
{
	register char ch(getc());
	while(!isgraph(ch)) ch = getc();
	for(; isgraph(ch); ch = getc()) *s++ = ch;
	*s = '\0';
	return s;
}

// END tpl.

const int MAXN = 6, MAXC = 50;

int n, C;

int L[MAXN + 5];

inline void input()
{
	n = read<int>(), C = read<int>();
	for(int i = 0; i < n; ++i) L[i] = read<int>();
}

inline void solve()
{
	sort(L, L + n);

	LD ans = 0;
	LL cnt = 0;
	do {
		const int U = (1 << n) - 1;

		static LL f[MAXC * MAXN + 5][1 << MAXN];
		memset(f, 0, sizeof f);

		f[L[n - 1] * n][1 << (n - 1)] = 1;
		for(int i = 0; i <= n * C; ++i)
			for(int j = i; j <= n * C; ++j) for(int S = 0; S < 1 << n; ++S) if(f[j][S])
			{
				int p = i % n - 1;
				if(p >= 0 && !(S >> p & 1)) f[min(n * C, max(j, i + L[p] * n))][S | 1 << p] += f[j][S];
			}
		++cnt, ans += f[n * C][U];
	} while(next_permutation(L, L + n - 1));

	ans /= cnt;
	for(int i = 1; i < n; ++i) ans /= C;
	printf("%.15Lf\n", ans);
}

int main()
{
#ifdef K_ON
	freopen("F.in", "r", stdin);
	freopen("F.out", "w", stdout);
#endif

	input();
	solve();

	return 0;
}