#include<bits/stdc++.h>

using namespace std;


int main(){
  int n;
  cin >> n;
  vector<long long> vc(n);
  set<long long> st;
  map<long long,long long> dp;
  map<long long,long long> ex;
  for(int i=0;i<n;i++){
    cin >> vc[i];
    st.insert(vc[i]);
    st.insert(vc[i]+1);
    dp[vc[i]]=1;
    ex[vc[i]]=1;
  }
  sort(vc.begin(),vc.end());
  long long res=0;
  for(auto k:st){
    if(k>=3){
      if(ex[k-1]==1){dp[k]+=dp[k-2];}
    }
    res+=dp[k];
  }
  cout << res << '\n';
}