#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  cin >> n >> m;
  vector<long long> A(n + 1, 0);
  int a;
  for (int i = 0; i < m; i++) {
    cin >> a;
    A[a] = -1;
  }
  vector<long long> dp(n + 1, 0);
  dp[0] = 1;
  dp[1] = (A[1] == 0);
  for (int i = 2; i <= n; i++) {
    if (A[i] == -1)
      dp[i] = 0;
    else {
      dp[i] = dp[i - 1] + dp[i - 2];
    }
  }
  cout << dp[n];
  return 0;
}
