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++14 (GCC 5.4.1) (judge verdict: Accepted)

#define _USE_MATH_DEFINES
#include<iostream>
#include<string>
#include<queue>
#include<cmath>
#include<map>
#include<set>
#include<list>
#include<iomanip>
#include<vector>
#include<random>
#include<functional>
#include<algorithm>
#include<stack>
#include<cstdio>
#include<bitset>
#include<unordered_map>
#include<climits>
#include<fstream>
using namespace std;
///////////////////library zone!!!!!!!!!!!!!!!!!!!!!!!!!!!!
typedef long long ll;
typedef long double ld;
#define all(a) (a).begin(),(a).end()
#define EPS (1e-5)
#define bit(n,k) ((n>>k)&1)
const ll Mod = 1000000007;
const ll mod = 998244353;
struct H {
	ll x, y;
	bool operator<(const H& b) const {
		if (x != b.x) return x < b.x;
		return y < b.y;
	}
	bool operator>(const H & b) const {
		if (x != b.x) return x > b.x;
		return y > b.y;
	}
	bool operator==(const H & b) const { return x == b.x && y == b.y; }
	bool operator!=(const H & b) const { return (*this) != b; }
};
struct P {
	ll pos, cost;
	bool operator<(const P& b) const { return cost < b.cost; }
	bool operator>(const P& b) const { return cost > b.cost; }
};
struct B {
	ll to, cost;
};
struct E {
	ll from, to, cost;
	bool operator<(const E& b) const { return cost < b.cost; }
	bool operator>(const E& b) const { return cost > b.cost; }
};
template<typename T, typename U>
void chmin(T & a, U b) {
	if (a > b) a = b;
}
template<typename T, typename U>
void chmax(T & a, U b) {
	if (a < b) a = b;
}
template<typename T>
T max_0(T a) {
	if (a < 0) return 0;
	return a;
}
template<typename T>
T min_0(T a) {
	if (a > 0) return 0;
	return a;
}
ll read() {
	ll u;
	ll k = scanf("%lld", &u);
	return u;
}
ll gcd(ll i, ll j) {
	if (i > j) swap(i, j);
	if (i == 0) return j;
	return gcd(j % i, i);
}
ll mod_pow(ll x, ll n, ll p) {
	ll res = 1;
	while (n > 0) {
		if (n & 1) res = res * x % p;
		x = x * x % p;
		n >>= 1;
	}
	return res;
}//x^n%p
const ll Inf = 3023372036854775807;
const int inf = 1500000000;
#define int long long
//----------------------------------------------------
int n, m;
int dp[200000];
bool a[200000];
signed main() {
	cin >> n >> m;
	for (int i = 0; i < m; i++) {
		a[read()] = 1;
	}
	dp[0] = 1;
	for (int i = 1; i <= n; i++) {
		if (a[i]) continue;
		dp[i] += dp[i - 1];
		if (i > 1) dp[i] += dp[i - 2];
		dp[i] %= Mod;
	}
	cout << dp[n] << endl;
}