Peter has a sequence of integers a1, a2, ..., an. Peter wants all numbers in the sequence to equal h. He can perform the operation of "adding one on the segment [l, r]": add one to all elements of the sequence with indices from l to r (inclusive). At that, Peter never chooses any element as the beginning of the segment twice. Similarly, Peter never chooses any element as the end of the segment twice. In other words, for any two segments [l1, r1] and [l2, r2], where Peter added one, the following inequalities hold: l1 ≠ l2 and r1 ≠ r2.

How many distinct ways are there to make all numbers in the sequence equal h? Print this number of ways modulo 1000000007 (109 + 7). Two ways are considered distinct if one of them has a segment that isn't in the other way.

Input

The first line contains two integers n, h (1 ≤ n, h ≤ 2000). The next line contains n integers a1, a2, ..., an (0 ≤ ai ≤ 2000).

Output

Print a single integer — the answer to the problem modulo 1000000007 (109 + 7).

Examples

Input

3 2
1 1 1


Output

4


Input

5 1
1 1 1 1 1


Output

1


Input

4 3
3 2 1 1


Output

0
import java.io.*;
import java.util.*;

public class D implements Runnable{
	public static void main (String[] args) {new Thread(null, new D(), "_cf", 1 << 28).start();}

	int n, h, a[], dp[][];
	int MOD = (int)1e9+7;
	
	public void run() {
		FastScanner fs = new FastScanner();
		PrintWriter out = new PrintWriter(System.out);
		System.err.println("Go!");

		n = fs.nextInt();
		h = fs.nextInt();
		a = fs.nextIntArray(n);
		dp = new int[n][n+1];
		for(int[] d : dp) Arrays.fill(d, -1);
		out.println(solve(0, 0));
		out.close();
	}

	int solve(int pos, int delta) {
		if(pos == n) {
			return delta == 0 ? 1 : 0;
		}
		if(dp[pos][delta] != -1) return dp[pos][delta];
		int res = 0;
		//start range
		if(a[pos]+delta+1 == h) res = add(res, solve(pos+1, delta+1));
		
		//stay same
		if(a[pos]+delta == h) res = add(res, solve(pos+1, delta));
		
		//start and end range
		if(a[pos]+delta+1 == h) res = add(res, mult(solve(pos+1, delta), 1));
		
		//end and start
		if(delta > 0 && a[pos]+delta+1 == h) res = add(res, mult(solve(pos+1, delta), delta));
		
		//end range
		if(delta > 0 && a[pos]+delta == h) res = add(res, mult(solve(pos+1, delta-1), delta));
		
		return dp[pos][delta] = res;
	}

	int add(int a, int b) {
		return (a+b)%MOD;
	}
	
	int mult(long a, long b) {
		a %= MOD; b %= MOD;
		a *= b;
		return (int)(a%MOD);
	}
	
	class FastScanner {
		public int BS = 1<<16;
		public char NC = (char)0;
		byte[] buf = new byte[BS];
		int bId = 0, size = 0;
		char c = NC;
		double num = 1;
		BufferedInputStream in;

		public FastScanner() {
			in = new BufferedInputStream(System.in, BS);
		}

		public FastScanner(String s) throws FileNotFoundException {
			in = new BufferedInputStream(new FileInputStream(new File(s)), BS);
		}

		public char nextChar(){
			while(bId==size) {
				try {
					size = in.read(buf);
				}catch(Exception e) {
					return NC;
				}                
				if(size==-1)return NC;
				bId=0;
			}
			return (char)buf[bId++];
		}

		public int nextInt() {
			return (int)nextLong();
		}

		public long nextLong() {
			num=1;
			boolean neg = false;
			if(c==NC)c=nextChar();
			for(;(c<'0' || c>'9'); c = nextChar()) {
				if(c=='-')neg=true;
			}
			long res = 0;
			for(; c>='0' && c <='9'; c=nextChar()) {
				res = (res<<3)+(res<<1)+c-'0';
				num*=10;
			}
			return neg?-res:res;
		}

		public double nextDouble() {
			double cur = nextLong();
			return c!='.' ? cur:cur+nextLong()/num;
		}

		public String next() {
			StringBuilder res = new StringBuilder();
			while(c<=32)c=nextChar();
			while(c>32) {
				res.append(c);
				c=nextChar();
			}
			return res.toString();
		}

		public String nextLine() {
			StringBuilder res = new StringBuilder();
			while(c<=32)c=nextChar();
			while(c!='\n') {
				res.append(c);
				c=nextChar();
			}
			return res.toString();
		}

		public boolean hasNext() {
			if(c>32)return true;
			while(true) {
				c=nextChar();
				if(c==NC)return false;
				else if(c>32)return true;
			}
		}
		
		public int[] nextIntArray(int n) {
			int[] res = new int[n];
			for(int i = 0; i < n; i++) res[i] = nextInt();
			return res;
		}
		
	}

}