#include<bits/stdc++.h>
using namespace std;
int a(int n){
  int r;
  if(n<3) r=1;
  else r=a(n-1)+a(n-2);
  return r;
  } 
int main(){
  int m;
  cin>>m;
  cout<<a(m)<<endl;
return 0;
}
/**************************************************************
	Problem: 1238
	User: wtq001
	Language: C++
	Result: Accepted
	Time:13 ms
	Memory:2072 kb
****************************************************************/