#include <algorithm>
#include <iostream>
#include <vector>

using namespace std;

typedef long long ll;
typedef pair<ll, ll> P;

#define MOD 1000000007
#define REP(i, N) for (int i = 0; i < N; ++i)
#define REP1(i, N) for (int i = 1; i <= N; ++i)
#define RREP(i, N) for (int i = N - 1; i >= 0; --i)
#define ALL(a) a.begin(), a.end()

ll dp[100];

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