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 C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Linq;
using System.Collections.Generic;

public class Hello{
    public static void Main(){
        var list=new List<double>();
        string[]array=Console.ReadLine().Split(' ');
        for(var i=0;i<array.Length;i++){
            list.Add(int.Parse(array[i]));
        }
        double N=list[0];
        double M=list[1];
        
        var flg=0;
        var list_list=new List<double>();
        for(var i=0;i<M;i++){
            list_list.Add(double.Parse(Console.ReadLine()));
            if(i>=1&&list_list[i]-list_list[i-1]==1){
                Console.WriteLine(0);
                flg=1;
                break;
            }
        }
        
        var list_main=new List<double>();
        double count=0;
        double sum=1;
        if(flg==0){
            for(var i=0;i<=N;i++){
                list_main.Add(i);
            }
            for(var i=0;i<M;i++){
                list_main.Remove(list_list[i]);
            }
            
            for(var i=0;i<list_main.Count;i++){
                if(i>0){
                    if(list_main[i]-list_main[i-1]!=1){
                        //Console.WriteLine(Fib(count));
                        sum=sum*(Fib(count));
                        count=1;
                    }
                    else if(i==list_main.Count-1){
                        //Console.WriteLine(Fib(count));
                        sum=sum*(Fib(count));
                    }
                }
                count++;
            }
            Console.WriteLine(sum%1000000007);
        }
    }
    
    public static double Fib(double a){
        if(a<=1){
            return a;
        }
        return Fib(a-1)+Fib(a-2);
    }
}