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 a1-th, a2-th, a3-th, \ldots, aM-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.
Input is given from Standard Input in the following format:
N M a1 a2 . . . aM
Print the number of ways to climb up the stairs under the condition, modulo 1\ 000\ 000\ 007.
6 1 3
There are four ways to climb up the stairs, as follows:
10 2 4 5
There may be no way to climb up the stairs without setting foot on the broken steps.
100 5 1 23 45 67 89
Be sure to print the count modulo 1\ 000\ 000\ 007.