#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
#else
  #define Debug(...) void(0)
#endif
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

int main() {
  int n;
  cin >> n;
  vector<ll> dp(n + 1, 0);
  dp[0] = 1;
  rep(i, n) {
    if (i + 1 <= n) dp[i + 1] += dp[i];
    if (i + 2 <= n) dp[i + 2] += dp[i];
  }
  cout << dp[n] << endl;
  return 0;
}