ek baar 3 lena h

#include<bits/stdc++.h>
using namespace std;


int solve(int n, int flag){
   if(n<=0)return 1;
   if(n == 1)return 1;
   if(n == 2)return 2;
   if(n == 3 && flag == 0)return 3;
   if(n == 3 && flag == 1)return 4;
   int ans = 0;
   if(flag == 0){
      return ans += solve(n-1,0) + solve(n-2,0);
   }
   else if(flag == 1){
      return ans +=  solve(n-1,1) + solve(n-2,1) + solve(n-3,0);
   }
   return ans;
}

int main(){
  int n; cin>>n;
  cout<<solve(n,1)<<endl;

   return 0;
}