//dfs暴搜＋记忆化搜索
#include<iostream>
#include<cstring>
using namespace std;

int dp[20];
int fun(int x)
{
  if(x<=2) return x;
  if(dp[x]!=-1) return dp[x];
  return dp[x]=fun(x-1)+fun(x-2);
}

int main()
{
  memset(dp, -1, sizeof(dp));
  int n; 
  cin >> n;
  int ans=fun(n);
  cout << ans;
  return 0;
}