#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <string>
#include <cmath>
#include <cstring>
#include <vector>


int main(){
  int n;
  std::cin >> n;
  long* dp = (long*)malloc((n+1) * sizeof(long));
  dp[0] = 1;
  for(register int i =1; i < n+1;i++){
    if(i > 1) dp[i] = dp[i-1]+ dp[i-2];
    else dp[i] += dp[i-1];
  }
  std::cout << dp[n]<< std::endl;
}