#include <algorithm>
#include <cmath>
#include <cstdio>
#include <deque>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>

using namespace std;

typedef long long ll;

#define MOD 1000000007

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