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

// macros
#define pb emplace_back
#define mk make_pair
#define FOR(i, a, b) for(int i=(a);i<(b);++i)
#define rep(i, n) FOR(i, 0, n)
#define rrep(i, n) for(int i=((int)(n)-1);i>=0;i--)
#define irep(itr, st) for(auto itr = (st).begin(); itr != (st).end(); ++itr)
#define irrep(itr, st) for(auto itr = (st).rbegin(); itr != (st).rend(); ++itr)
#define whole(x) (x).begin(),(x).end()
#define sz(x) ((int)(x).size())
#define bit(n) (1LL<<(n))
// functions
template <typename T> void unique(T& c){c.erase(std::unique(c.begin(), c.end()), c.end());}
template <class T>bool chmax(T &a, const T &b){if(a < b){a = b; return 1;} return 0;}
template <class T>bool chmin(T &a, const T &b){if(a > b){a = b; return 1;} return 0;}
template <typename T> istream &operator>>(istream &is, vector<T> &vec){for(auto &v: vec)is >> v; return is;}
template <typename T> ostream &operator<<(ostream &os, const vector<T>& vec){for(int i = 0; i < vec.size(); i++){ os << vec[i]; if(i + 1 != vec.size())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const set<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const unordered_set<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const multiset<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T> ostream &operator<<(ostream &os, const unordered_multiset<T>& st){for(auto itr = st.begin(); itr != st.end(); ++itr){ os << *itr; auto titr = itr; if(++titr != st.end())os << " ";} return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &p){os << "(" << p.first << ", " << p.second << ")"; return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const map<T1, T2> &mp){for(auto itr = mp.begin(); itr != mp.end(); ++itr){ os << "(" << itr->first << ", " << itr->second << ")"; auto titr = itr; if(++titr != mp.end())os << " "; } return os;}
template <typename T1, typename T2> ostream &operator<<(ostream &os, const unordered_map<T1, T2> &mp){for(auto itr = mp.begin(); itr != mp.end(); ++itr){ os << "(" << itr->first << ", " << itr->second << ")"; auto titr = itr; if(++titr != mp.end())os << " "; } return os;}
//  types
using ll = long long int;
using P = pair<int, int>;
// constants
const int inf = 1e9;
const ll linf = 1LL << 50;
const double EPS = 1e-10;
const int mod = 1000000007;
const int dx[4] = {-1, 0, 1, 0};
const int dy[4] = {0, -1, 0, 1};
// io
struct fast_io{
  fast_io(){ios_base::sync_with_stdio(false); cin.tie(nullptr); cout << fixed << setprecision(20);}
} fast_io_;

ll memo[101];
ll fib(int i){
  if(memo[i] > 0)return memo[i];
  if(i <= 1)return memo[i] = 1;
  return memo[i] = fib(i-1) + fib(i-2);
}

int main(int argc, char const* argv[])
{
  int n; cin >> n;
  cout << fib(n) << endl;
  return 0;
}

C++: // input: aldsalds1_10_a.in
#include<iostream>
#define MAX_N 44
#define NIL -1
using namespace std;

int dp[MAX_N];

int fib(int n) {
  if(n == 0 || n == 1)
    return 1;

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

  return fib(n-1) + fib(n-2);
}

int main() {
  for(int i=0; i<MAX_N; i++)
    dp[i] = NIL;

  int x;
  cin >> x;

  cout << fib(x) << endl;
}

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



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

    ll fib[N+1];
    fib[0] = 1;
    fib[1] = 1;

    for (int i=2; i<=N; i++) fib[i] = fib[i-1] + fib[i-2];

    cout << fib[N] << endl;

    return 0;
}

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

long long n;
vector<long long> f;

long long calc(long long x) {
  if(f[x] != -1) return f[x];
  return f[x] = calc(x - 1) + calc(x - 2);
}

int main() {
  cin >> n;
  f.assign(n + 1, -1);
  f[0] = f[1] = 1;
  cout << calc(n) << endl;
  return 0;
}

C++: #include<iostream>
#include <string>
using namespace std;
int a,ans[46];
int main(){
	cin>>a;
	ans[0]=1,ans[1]=2;
	for(int i=0;i<a;i++){
	ans[i+2]=ans[i+1]+ans[i];}
	cout<<ans[a-1]<<endl;
		    return 0;
	}

C++: #include <iostream>
 
using namespace std;
 
typedef unsigned long long ull;
 
auto fib(ull const n) -> ull
{
    return ( n == 1 || n == 0 ) ? n : fib( n - 1 ) + fib( n - 2 );
}
 
int main()
{
    ull n;
    cin >> n;
    cout << fib( n ) << endl;
}

C++: #include<iostream>

using namespace std;

int fib(int n);

int main() {
  int n;

  //入力
  cin >> n;

  //出力
  cout << fib(n) << endl;

  return 0;
}

int fib(int n){
  int dp[1000];
  dp[0] = 1;
  dp[1] = 1;

  for(int i = 2; i <= n; i++){
    dp[i] = dp[i-1] + dp[i-2];
  }
  return dp[n];
}

C++: #include<stdio.h>
#include<iostream>
#include<string>
#include<algorithm>
using namespace std;

int main(){
	
	int n[47];
	n[1]=1;n[2]=2;

	for(int i=3;i<=45;i++)
		n[i]=n[i-1]+n[i-2];

	cout<<n[44]<<endl;
	return 0;
}

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

#define INF 1e9
vector<int> memo;

int fib(int n){
  if(memo[n] == -INF){ memo[n] = fib(n - 1) + fib(n - 2); }
  return memo[n];
}

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

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

constexpr ll DP_MAX = 1000000;
ll dp[DP_MAX];

int main(int argc, char **argv)
{
	ll n; cin >> n;
	memset(dp, 0, sizeof dp);
	dp[0] = dp[1] = 1;
	for (ll i = 2; i <= n; ++i)
		dp[i] = dp[i-1] + dp[i-2];
	std::cout << dp[n] << std::endl;
}

C++: #include<iostream>

using namespace std;

int fib(int n);

int main() {
  int n;

  //入力
  cin >> n;

  //出力
  cout << fib(n) << endl;

  return 0;
}

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

C++: #include <iostream>
#include <vector>

using namespace std;

int main(){
  int n; cin >> n;
  vector<int> fib;
  fib.push_back(0); fib.push_back(1);

  for(int i=0; i<n; i++)
    fib.push_back(fib[i]+fib[i+1]);

  cout << fib.back() << endl;

  return 0;
}

C++: #include <iostream>

using namespace std;

int memo[45];

int fibonacchi(int num)
{
    if (memo[num] != -1) {
        return memo[num];
    } else if (num == 0 || num == 1) {
        memo[num] = 1;
        return memo[num];
    } else {
        int result = fibonacchi(num - 1) + fibonacchi(num - 2);
        memo[num] = result;
        return memo[num];
    }
}

int main()
{
    for (int i = 0; i < 45; ++i)
        memo[i] = -1;

    int n;
    cin >> n;
    cout << fibonacchi(n) << '\n';
}

C++: #include<stdio.h>

int main()
{
	int fib1{ 1 }, fib2{ 1 }, n;

	scanf("%d", &n);
	for (int i = 1; i < n; ++i)
	{
		int tmp = fib2;
		fib2 += fib1;
		fib1 = tmp;
	}
	printf("%d\n", fib2);
	return 0;
}