#include <bits/stdc++.h>
using namespace std;
using Graph = vector<vector<int>>;
using PAIR = pair<string, int>;
const int mod = 1000000007;
struct mint {
  long long x;
  mint(long long x = 0) : x((x % mod + mod) % mod) {}
  mint operator-() const { return mint(-x); }
  mint &operator+=(const mint a) {
    if ((x += a.x) >= mod) x -= mod;
    return *this;
  }
  mint &operator-=(const mint a) {
    if ((x += mod - a.x) >= mod) x -= mod;
    return *this;
  }
  mint &operator*=(const mint a) {
    (x *= a.x) %= mod;
    return *this;
  }
  mint operator+(const mint a) const { return mint(*this) += a; }
  mint operator-(const mint a) const { return mint(*this) -= a; }
  mint operator*(const mint a) const { return mint(*this) *= a; }
  mint pow(long long t) const {
    if (!t) return 1;
    mint a = pow(t >> 1);
    a *= a;
    if (t & 1) a *= *this;
    return a;
  }
  mint inv() const { return pow(mod - 2); }
  mint &operator/=(const mint a) { return *this *= a.inv(); }
  mint operator/(const mint a) const { return mint(*this) /= a; }
};
istream &operator>>(istream &is, const mint &a) { return is >> a.x; }
ostream &operator<<(ostream &os, const mint &a) { return os << a.x; }
int main() {
  int n, m;
  cin >> n >> m;
  vector<long long> dp(n + 10, 0);
  for (int i = 0; i < m; i++) {
    int a;
    cin >> a;
    dp[a] = -1;
  }
  dp[0] = 1;
  for (int i = 1; i <= n; i++) {
    if (dp[i] != -1) {
      if (i != 1) {
        if (dp[i - 1] == -1 && dp[i - 2] == -1) {
          cout << -1 << endl;
          return 0;
        }
        dp[i] = (max(dp[i - 1], 0ll) + max(dp[i - 2], 0ll)) % mod;
      } else {
        dp[i] = max(dp[i - 1], 0ll);
      }
    }
  }
  cout << dp[n] % mod << endl;
  return 0;
}
