#include <iostream>
#include <string>
#include <vector>
#include <queue>
#include <deque>
#include <algorithm>
#include <set>
#include <map>
#include <bitset>
#include <cmath>
#include <functional>
#include <iomanip>
#define vll vector<ll>
#define vvvl vector<vvl>
#define vvl vector<vector<ll>>
#define VV(a, b, c, d) vector<vector<d>>(a, vector<d>(b, c))
#define VVV(a, b, c, d) vector<vvl>(a, vvl(b, vll (c, d)));
#define re(c, b) for(ll c=0;c<b;c++)
#define rep(a,b,c) for(ll a=b;a<c;a++)
#define all(obj) (obj).begin(), (obj).end()
typedef long long int ll;
typedef long double ld;
using namespace std;

void get(vll &a){re(i,a.size()) scanf("%lld",&a[i]);}
void get(vvl &a){re(i,a.size()) re(j,a[0].size()) scanf("%lld",&a[i][j]);}
void print(vll &a){re(i,a.size()) cout<<a[i]<<(i==a.size()-1?"\n":" ");}
void print(vvl &a){re(i,a.size()) re(j,a[0].size())cout<<a[i][j]<<(j==a[0].size()-1?"\n":" ");}


ll gcd(ll _a, ll _b) {
  unsigned long long a = abs(_a), b = abs(_b);
  if(a == 0) return b;
  if(b == 0) return a;
  int shift = __builtin_ctzll(a | b);
  a >>= __builtin_ctzll(a);
  do {
    b >>= __builtin_ctzll(b);
    if(a > b) std::swap(a, b);
    b -= a;
  }while(b);
  return (a << shift);
}
int main(int argc, char const *argv[]) {
  ll n;std::cin >> n;
  vll a(n+1, 0);
  a[0] = a[1] = 1;
  for(int i=2;i<=n;i++) a[i] = a[i-1] + a[i-2];
  std::cout << a[n] << '\n';
}