#include <bits/stdc++.h>
#define all(x) (x).begin(), (x).end()
using namespace std;
typedef long long ll;

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