#include<bits/stdc++.h>
using namespace std;
#define int long
main(){
  int n,m,c;
  cin>>n>>m;
  vector<int> dp(n+1,0);
  map<int,bool> a;
  for(int i=0;i<m;++i){
    cin>>c;
    a[c]=true;
  }
  dp[0]=1;
  for(int i=0;i<=n;++i){
    if(i+2<=n&&!a[i+2])dp[i+2]+=dp[i];
    if(i+1<=n&&!a[i+1])dp[i+1]+=dp[i];
  }
  cout<<dp[n];
}