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 Pascal (FPC 2.6.2) (judge verdict: Wrong Answer)

var a,b,c,n,M,r,i:int64;    //a=a_i、b=a_i-1
    G:array[1..100000] of integer;
begin 
 read(N,M);

  G[1]:=1;G[2]:=1;    //フィボナッチ数列を準備
 for i := 3 to N do
  G[i] := G[i-1] + G[i-2];
 
 n:=1; read(a);     
 if a=1 then c:=1 else c:= a-1;
    n:=n*G[c]; b:=a;
 
 for i := 2 to M do
 begin
   read(a); c:= a-b-1; n:= n*G[c] mod 1000000007;
 end;
 
write(r)
end.