Go: package main

// import (
// 	"fmt"
// 	"bufio"
// 	"strconv"
// 	"os"
// )

// func fib(n int) int{
// 	if n == 0 || n == 1{
// 		return 1
// 	} else {
// 		return fib(n-1) + fib(n-2)
// 	}
// }

// func main(){
// 	sc := bufio.NewScanner(os.Stdin)
// 	sc.Scan()
// 	n, _ := strconv.Atoi(sc.Text())
// 	fmt.Println(fib(n))
// }

import (
	"fmt"
)

func main(){
	var n, pre1, pre2, now int
	fmt.Scan(&n)
	if n == 0 || n == 1{
		fmt.Println(1)
	} else {
		pre1, pre2 = 1, 1
		for i:=1; i<n; i++{
			now = pre1 + pre2
			pre2 = pre1
			pre1 = now
		}
		fmt.Println(now)
	}

}

C++: /**Function Template**/
#include<bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef pair<ll,ll> pint;
const int MAX = 510000;
const int MOD = 1000000007;
#define rep(i, n) for(ll i = ll(0); i < ll(n); i++)
#define Rep(i, n) for(ll i = ll(1); i < ll(n); i++)
#define ALL(a)  (a).begin(),(a).end()
#define IOS ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define PI 3.14159265358979323846
#define ifYN(x) cout<<(x?"Yes":"No")<<"\n" 
ll fac[MAX], finv[MAX], inv[MAX];


template<class T> inline bool chmin(T& a, T b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}
template<class T> inline bool chmax(T& a, T b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}

bool palindrome(string s){
  bool flag=true;
  rep(i,(ll)s.size()) if(s[i]!=s[s.size()-1-i]) flag=false;
  return flag;
}

// テーブルを作る前処理
void COMinit() {
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for (ll i = 2; i < MAX; i++){
        fac[i] = fac[i - 1] * i % MOD;
        inv[i] = MOD - inv[MOD%i] * (MOD / i) % MOD;
        finv[i] = finv[i - 1] * inv[i] % MOD;
    }

}
ll Len(ll n) {
  ll s=0;
  while(n!=0) s++, n/=10;
  return s;
}


ll Sint(ll n) {
  ll ans=0;
  while(n!=0) ans+=n%10,n/=10;
  return ans;
}

ll Svec(vector<ll> v){
  ll n=0;
  rep(i,(ll)v.size()) n+=v[i];
  return n;
}


ll GCD(ll a,ll b) {
  return b ? GCD(b,a%b) : a;
}


ll LCM(ll a,ll b){
  return a/GCD(a,b)*b;
}


ll Factorial(ll n){
  ll m=1;
  while(n>=1) m*=n,n--;
  return m;
}

void runlength(string s,vector<pair<char,ll>> &p){
  ll x=1;
  if(s.size()==1){
    p.push_back(pair<char,ll>(s[0],1));
  }
  rep(i,(ll)s.size()-1){
    if(s[i]==s[i+1]){
      x++;
      if(i==(ll)s.size()-2){
        p.push_back(pair<char,ll>(s[i],x));
      }
    }else{
      p.push_back(pair<char,ll>(s[i],x));
      x=1;
      if(i==(ll)s.size()-2){
        p.push_back(pair<char,ll>(s[s.size()-1],x));
      }
    }
  }
}

ll COM(ll n,ll k){
    if (n < k) return 0;
    if (n < 0 || k < 0) return 0;
    return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}

ll modpow(ll a, ll n, ll mod) {
    ll res = 1;
    while (n > 0) {
        if (n & 1) res = res * a % mod;
        a = a * a % mod;
        n >>= 1;
    }
    return res;
}

string Toupper(string s){
  string ans="";
  rep(i,s.size()){
    if('a'<=s[i] && s[i]<='z') ans+=(char)s[i]-32;
    else ans+=s[i];
  }
  return ans;
}
string Tolower(string s){
  string ans="";
  rep(i,s.size()){
    if('A'<=s[i] && s[i]<='Z') ans+=(char)s[i]+32;
    else ans+=s[i];
  }
  return ans;
}

void dis(vector<ll> v){ rep(i,v.size()) cout<<v[i]<<endl; }

void dis2(vector<vector<ll>> v){
  rep(i,v.size()){
    rep(j,v[0].size()) cout<<v[i][j]<<' ';
    cout<<endl;
  }
}

const int MAX_N=100010;
vector<bool> sieve_of_eratosthenes(){
  vector<bool> isPrime(MAX_N+1,true);
  /* isPrime[1]=false; */
  for(int i=2;i<=MAX_N;i++){
    if(isPrime[i]){
      for(int j=2*i;j<=MAX_N;j+=i){
        isPrime[j]=false;
      }
    }
  }
  return isPrime;
}

vector<pint> prime_factorize(ll n){
  vector<pint> ans;
  for(ll p=2;p<=sqrt(n);p++){
    if(n%p!=0) continue;
    ll cnt=0;
    while(n%p==0){
      n/=p;
      cnt++;
    }
    ans.push_back(make_pair(p,cnt));
  }
  if(n!=1) ans.push_back(make_pair(n,1));
  return ans;
}

/*bool cmp(pint a, pint b) { return a.second < b.second; }*/

/*↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓*/
int main() {
  IOS;
  ll n;
  cin>>n;
  vector<ll> dp(100,0);
  dp[0]=1,dp[1]=1;
  rep(i,50) dp[i+2]=dp[i]+dp[i+1];
  cout<<dp[n]<<endl;
}

C++: #include <iostream>
using namespace std;
int n;
int fib(int n){
	if(n == 0 || n == 1) return 1;
	else{
	return fib(n-1) + fib(n-2);
	}
}

int main(){
	cin >> n;
	cout << fib(n) <<endl;
	return 0;
}

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

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

    int F[50];
    F[0] = F[1] = 1;

    for (int i = 2; i <= n; i++)
        F[i] = F[i - 1] + F[i - 2];

    cout << F[n] << endl;
}

C++: #include <iostream>
using namespace std;

int main () {
	int n;
	cin >> n;
	int F[50];
	F[0] = F[1] = 1;
	for (int i=2; i<=n; ++i) F[i] = F[i-1] + F[i-2];
	cout << F[n] << endl;
	return 0;
}

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

int fib(int n){
  if (n <= 1) return (1);
  else  return (fib(n - 1) + fib (n - 2));
}

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

  cout << fib(n) << endl;
  return (0);
}

C++: #include<iostream>

using namespace std;

int main(){
  int n;cin >> n;
  long long a=1, b=1, c;
  for(int i=0;i<n-1;i++){
    c = b;
    b = a;
    a = b + c;
  }
  cout << a << endl;
}

C++: #include <iostream>
#include <vector>
using namespace std;

using ll = long long;

vector<ll> F(45, 0);
long fibDP(int n) {
	if(n <= 1) return F[n] = 1;
	if(F[n] != 0) return F[n];
	return F[n] = fibDP(n-1) + fibDP(n-2);
}

int main() {
	int n; cin >> n;
	cout << fibDP(n) << endl;
	return 0;
}

C++: #include <iostream>

using namespace std;

const int N = 45;
int fib[N];

int main()
{
    int n;
    scanf("%d", &n);
    fib[0] = fib[1] = 1;
    for (int i = 2; i <= n; i++)
    {
        fib[i] = fib[i-1] + fib[i-2];
    }
    printf("%d\n", fib[n]);
    return 0;
}

C++: #include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (n); ++i)
using namespace std;

int main() {
  int n;
  cin >> n;
  vector<int> fib(n + 1);
  fib[0] = 1;
  fib[1] = 1;
  rep(i, n - 1) fib[i + 2] = fib[i + 1] + fib[i];
  cout << fib[n] << endl;
  return 0;
}

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

int main(){
    int n;
    cin >> n;
    int a1 = 1, a2 = 1, temp;
    for(int i = 1; i < n; i++){
        temp = a2;
        a2 += a1;
        a1 = temp;
    }
    printf("%d\n", a2);
    return 0;
}

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

int A[2000000],N = 0,dp[45];

int fibonacci(int n) {

  if(dp[n] != 0) return dp[n];

  if(n == 0 || n == 1) return dp[n] = 1;
  else return dp[n] = fibonacci(n - 1) + fibonacci(n - 2);
}


int main() {

  int N;
  cin >> N;

  int ans = fibonacci(N);
  cout << ans << endl;

}

C++: #include <iostream>

int Fib[45];

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

  Fib[0]=Fib[1]=1;
  for(int i=2; i<=n; i++){
    Fib[i] = Fib[n-1]+Fib[i-2];
  }
  std::cout << Fib[n] << std::endl;

  return 0;
}