#include <bits/stdc++.h>

using namespace std;
typedef long long ll;

int n;
ll dp[51];

int main() {
  cin >> n;
  dp[0] = 1;
  for (int i = 1; i <= n; i++) {
    if (i - 1 >= 0) dp[i] += dp[i - 1];
    if (i - 2 >= 0) dp[i] += dp[i - 2];
  }
  cout << dp[n] << endl;

  return 0;
}