#include <bits/stdc++.h>
using namespace std;

//{{{
/********************************************************************/
struct Fast {Fast(){std::cin.tie(0);ios::sync_with_stdio(false);}} fast;

typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<vector<int> > vii;
typedef queue<int> qi;
typedef stack<int> si;
typedef deque<int> dqi;

#define reps(i, a, b) for (int i = a; i < b; ++i)
#define rep(i, n) reps(i, 0, n)
#define REPS(i, a, b) reps(i, a, b)
#define REP(i, n) rep(i, n)
#define deps(i, a, b) for (int i = a; i >= b; --i)
#define dep(i, n) deps(i, n, 0)
#define DEPS(i, a, b) deps(i, a, b)
#define DEP(i, n) dep(i, n)

#define pf push_front
#define pb push_back
#define mp make_pair
#define fst first
#define FST fst
#define sec second
#define SEC sec
#define sz(obj) ((int)(obj).size())
#define all(v) (v).begin(), (v).end()
#define ALL(v) all(v)
#define endl '\n'

const int INF = 999999999;
const int MOD = 1e9 + 7;
const int dx[] = {0, 1, 0, -1, 1, 1, -1, -1}, dy[] = {1, 0, -1, 0, 1, -1, -1, 1};

inline bool inside(int y, int x, int H, int W) { return y >= 0 && x >= 0 && y < H && x < W; }
inline int in() { int x; std::cin >> x; return x; }
template <typename T>
void print(std::vector<T>& v, char c = ' ') {
  REP(i, v.size()) {
    if (i != 0) std::cout << c;
    std::cout << v[i];
  }
  std::cout << '\n';
}
template <typename T> void print(T x) { std::cout << x << '\n'; }

/****************************************************************/
//}}}

long long int a[55];
signed main()
{
  int n = in();
  a[0] = 1;

  for (int i = 0; i < n; i++) {
    for (int j = 1; j <= 2; j++) {
      a[i + j] += a[i];
    }
  }
  cout << a[n] << endl;

  return (0);
}