Problem:
Score : 300 points

Problem Statement

There is a staircase with N steps. Takahashi is now standing at the foot of the stairs, that is, on the 0-th step.
He can climb up one or two steps at a time.

However, the treads of the a_1-th, a_2-th, a_3-th, \ldots, a_M-th steps are broken, so it is dangerous to set foot on those steps.

How many are there to climb up to the top step, that is, the N-th step, without setting foot on the broken steps?
Find the count modulo 1\ 000\ 000\ 007.

Constraints

1 \leq N \leq 10^5

0 \leq M \leq N-1

1 \leq a_1 < a_2 < ... < a_M \leq N-1

Input

Input is given from Standard Input in the following format:

N M
a_1
a_2
.
.
.
a_M

Output

Print the number of ways to climb up the stairs under the condition, modulo 1\ 000\ 000\ 007.

Sample Input 1

6 1
3

Sample Output 1

4

There are four ways to climb up the stairs, as follows:

0 \to 1 \to 2 \to 4 \to 5 \to 6

0 \to 1 \to 2 \to 4 \to 6

0 \to 2 \to 4 \to 5 \to 6

0 \to 2 \to 4 \to 6

Sample Input 2

10 2
4
5

Sample Output 2

0

There may be no way to climb up the stairs without setting foot on the broken steps.

Sample Input 3

100 5
1
23
45
67
89

Sample Output 3

608200469

Be sure to print the count modulo 1\ 000\ 000\ 007.

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Runtime Error)

import java.util.Scanner;
public class Main {
	public static boolean Esta(int k, int[]A) {
		for(int i=0;i<A.length;i++) {
			if (A[i]==k){
				return true;
			}
		}
		return false;
	}
	public static void main(String[] args) {
		Scanner s = new Scanner(System.in);
		String[] linea = s.nextLine().split(" ");
		int N=Integer.parseInt(linea[0]);
		int M=Integer.parseInt(linea[1]);
		int [] A= new int[(int)(M+1)];
		for(int i=1; i<=M;i++) {
			String[] linea2 = s.nextLine().split(" ");
			A[i]=Integer.parseInt(linea2[0]);
			
		}
		s.close();
		long []DP= new long[N+1];
		DP[1]=1;
		DP[2]=2;
		boolean a=true;
		for(int j=1;j<M;j++) {
			if(A[j+1]-A[j]==1 && j!=1) {
				System.out.print(0);
				a=false;
				break;
			}
			}
		if(Esta(1,A)) {
			DP[2]=1;
			DP[1]=0;
		}
		for(int k=3;k<=N;k++) {
			if(Esta(k,A)) {
				DP[k]=0;
			}
			else {
				DP[k]=DP[k-1]+DP[k-2];
			}
		}
		if(a) {
			System.out.print(DP[N]%1000000007);
		}
		}}