#define REP(i, n) for (int i = 0; i < (n); i++)
#define RREP(i, a, b) for (int i = a; i < (b); i++)
#define FOR(i, n) for (int i = n; i >= 0; i--)
#include <algorithm>
#include <cmath>
#include <cstdio>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <stack>
#include <string>
#include <vector>
#define SIZE 100001
#define MOD 1000000007
#define INF 100000000
using namespace std;

int main() {
  int n;
  cin >> n;

  long long dp[51];
  REP(i, 51) dp[i] = 0;
  dp[1] = 1;
  dp[2] = 2;

  RREP(i, 3, 51) dp[i] = dp[i - 1] + dp[i - 2];

  cout << dp[n] << endl;
  return 0;
}