#include <bits/stdc++.h>

using namespace std;
typedef long long ll;

int n;
ll dp[60];

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

  return 0;
}