#include <bits/stdc++.h>
using namespace std;
int main() {
  int N, M;
  cin >> N >> M;
  vector<int> a;
  a.push_back(-1);
  int b;
  cin >> b;
  a.push_back(b);
  int beforeEmpty = b;
  for (int i = 1; i < M; i++) {
    int s;
    cin >> s;
    if (beforeEmpty + 1 == s) {
      cout << 0;
      return 0;
    }
    a.push_back(s);
    beforeEmpty = s;
  }
  a.push_back(N + 1);
  vector<int> buf;
  buf.push_back(1);
  buf.push_back(1);
  for (int i = 2; i < N; i++) {
    int push = buf[i - 1] + buf[i - 2];
    for (int j = 0; j < a.size(); j++) {
      if (i == a[j]) {
        push = 0;
        break;
      }
    }
    buf.push_back(push);
  }
  cout << buf[N - 1];
}
