#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
ll dp[105][105];
int main() {
  int n;

  cin >> n;
  dp[0][0] = 1;

  for(int i = 0; i < n; i++) {
    for(int j = 0; j < n; j++) {
      if(j + 1 <= n) {
	dp[i+1][j+1] += dp[i][j];
      }
      if(j + 2 <= n) {
	dp[i+1][j+2] += dp[i][j];
      }
    }
  }

  ll ans = 0;
  for(int i = 0; i <= n; i++) ans += dp[i][n];

  cout << ans << endl;
}