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++: #include <bits/stdc++.h>

#define rep(i, a, b) for (int i = a; i < (int)(b); ++i)
#define rrep(i, a, b) for (int i = b - 1; i >= (int)(a); --i)

using namespace std;

using ll = long long;
using vi = vector<int>;
using vll = vector<ll>;

int calc_memo(vi& dp, int n) {
    if (n <= 1) { return 1; }
    if (dp[n] != 0) { return dp[n]; }
    return dp[n] = calc_memo(dp, n - 2) + calc_memo(dp, n - 1);
}

int calc_dp(vi& dp, int n) {
    dp[0] = dp[1] = 1;
    int i = 2;
    while(i <= n) {
        dp[i] = dp[i - 1] + dp[i - 2];
        ++i;
    }
    return dp[i - 1];
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);

    int n;
    cin >> n;

    vi dp(n + 1, 0);
    cout << calc_dp(dp, n) << endl;

    return 0;
}

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]<<"\n";
    return 0;
}

C++: #include <iostream>

using namespace std;

int main(){
  int n;
  unsigned long long fib[50];
  
  fib[0] = 1;
  fib[1] = 1;

  cin >> n;

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

  cout << fib[n] << endl;

  return 0;
}

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

int main()
{
	int n,i;
	int a[44];
	cin >> n;
	a[0]=1;
	a[1]=1;
	for(i=2;i<n;i++){
		a[i]=a[i-1]+a[a-2];
	}
	cout << a[n-1]<<endl;

}

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

int main(){
int i,fib[45],n;
cin>>n;
fib[0]=1,fib[1]=1;
for(i=2;i<=n;i++){
fib[i]=fib[i-1]+fib[i-2];
}
cout<<fib[n]<<endl;
}

C++: #include <bits/stdc++.h>
using namespace std;
#define MAX 50
int fibonacci(int);
int F[MAX];

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

int fibonacci(int n){
  if(n == 0 || n == 1){
    return F[n] = 1;
  }
  if(F[n] != -1){
    return F[n];
  }
  return F[n] = fibonacci(n-2) + fibonacci(n-1);
}

C++: // -*- coding: utf-8 -*-
// Last-Updated : <2014/06/20 08:35:59 by samui>

#include <algorithm>
#include <iostream>
#include <cstdio>
#include <string>
#include <vector>
#include <climits>
#include <set>
#include <bitset>

#define MP(a, b) std::make_pair(a, b)
#define X first
#define Y second
#define rep(i,n) for(int (i) = 0; (i) < (int)(n); ++(i))
#define rer(i,l,n) for(int (i) = l; (i) <= (int)(n); ++(i))
#define reu(i,l,n) for(int (i) = l; (i) < (int)(n); ++(i))
template<typename T,typename U> inline void amin(T &x,U y){ if(y<x) x = y;}
template<typename T,typename U> inline void amax(T &x,U y){ if(x<y) x = y;}
template<typename TYPE,std::size_t SIZE>
std::size_t len(const TYPE (&array)[SIZE]){return SIZE;}

// 幾何ライブ
typedef long double LD;
const LD INF = 1e100;
const LD EPS = 1e-8;
const LD PI = acos(-1);
typedef std::pair<LD,LD> PLD;
typedef std::vector<std::pair<LD,LD>> VPLD2;

class Point{
public:
  LD x,y;
  Point(LD x = 0,LD y = 0): x(x),y(y){ };
  Point operator + (Point p) {return Point(x+p.x,y+p.y);};
  Point operator - (Point p) {return Point(x-p.x,y-p.y);};
  Point operator * (LD a) {return Point(x*a,y*a);};
  Point operator / (LD a) {return Point(x/a,y/a);};
  LD abs(){return std::sqrt(x*x+y*y);};
  Point unit(){LD u = abs();return Point(x,y)/u; };
};
typedef Point Vector2D;
LD dotProduct(const Vector2D a,const Vector2D b){
  return a.x*b.x+a.y*b.y;
}
LD crossProduct(const Vector2D a, const Vector2D b){return a.x*b.y-a.y*b.x;}
LD angle(Vector2D a,Vector2D b){
  return acos(dotProduct(a,b)/(a.abs()*b.abs()));
}
LD norm(Vector2D a){return a.x*a.x+a.y*a.y;}
Point projection(Point a1,Point a2,Point a3){
  // 点a3にたいする線分a1-a2上への射影をもとめる。
  LD d = dotProduct(a3-a1,a2-a1)/norm(a2-a1);
  return (a1+(a2-a1)*d);
}
Point reflection(Point a1,Point a2,Point a3){
  return (a3+(projection(a1,a2,a3)-a3)*2);
}
int ccw(Point a1,Point a2,Point a3){
  Vector2D a = a2-a1;
  Vector2D b = a3-a1;
  if(crossProduct(a,b) > EPS) return 1; // a1,a2,a3が反時計まわり
  if(crossProduct(a,b) < -EPS) return -1;//a1,a2,a3が時計まわり
  if(dotProduct(a,b) < -EPS) return +2; //a3--a1--a2 で直線
  if(norm(a)< norm(b)) return -2; // a1--a2--a3 の順で直線
  return 0; // a1--a3--a2の順番
}


int main(int argc, char *argv[])
{
  int a[45];
  a[0] = 0;
  a[1] = 1;
  reu(i,2,46){
    a[i] = a[i-1]+a[i-2];
  }
  int t;
  std::cin>>t;
  std::cout<<a[t+1]<<std::endl;

  return 0;
}

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


void fibonacci(int n){
  vector<int> fib;

  fib.push_back(1);
  fib.push_back(1);

  if(n < 2){
    cout << "1" << endl;
  }else if(n == 2){
    fib.push_back(fib.at(0) + fib.at(1));
  }else{
    for(int i = 2;i < n+1;i++){
      fib.push_back(fib.at(i - 2) + fib.at(i - 1));
    }
  }

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

}

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

  return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vi = vector<int>;
using vvi = vector<vi>;
using vs = vector<string>;
using msi = map<string, int>;
using mii = map<int, int>;
using psi = pair<string, int>;
using pii = pair<int, int>;
using vlai = valarray<int>;
#define rep(i,n) for(int i=0;i<n;i++)
#define range(i,s,n) for(int i=s;i<n;i++)
#define all(a) a.begin(),a.end()
#define rall(a) a.rbegin(),a.rend()
#define fs first
#define sc second
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define INF 1E9
#define EPS 1E-9
#define MOD (1E9+7)
#define PI 3.1415926535897932384626433832795

std::ostream &operator<<(std::ostream &out, const vector<int> &tgt)
{
	string s;
	for (int i = 0; i<tgt.size(); i++) {
		s += (to_string(tgt[i]) + ((i != tgt.size() - 1) ? " " : ""));
	}
	out << s;
	return out;
}

int main() {
	int n;
	vi fib(45,1);
	for (int i = 2; i < 45; i++) {
		fib[i] = fib[i - 1] + fib[i - 2];
	}
	cin >> n;
	cout << fib[n] << endl;
}

C++: #include <iostream>
#include <stdlib.h>

using namespace std;

int F[44] = {0};

int Fib(int n){

	if(n == 0 || n == 1){
		return (F[n] = 1);
	}

	if(F[n] == 1){
		return F[n];
	}

	return (F[n] = Fib(n-1)+Fib(n-2));
}

int main(){

	int n;

	cin >> n;

	cout << Fib(n) << endl;

	return 0;
}

C++: #define _USE_MATH_DEFINES
#include <iostream>
#include <fstream>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cstring>
#include <cassert>
#include <string>
#include <vector>
#include <utility>
#include <complex>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <deque>
#include <tuple>
#include <bitset>
#include <limits>
#include <algorithm>
#include <array>
#include <random>
#include <complex>
#include <regex>
#include <iomanip>
using namespace std;
typedef long double ld;
typedef long long ll;
typedef vector<int> vint;
typedef vector<ll> vll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
#define fcout cout << fixed << setprecision(10)
#define rep(i,n)    for(int i=0; i<(int)n; i++)
#define mp(a,b) make_pair(a,b)
#define pb push_back
#define all(x) x.begin(), x.end()
const ll inf = 1e18;
const ll mod = 1e9 + 7;

int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};

int main(){
    int n;
    cin >> n;
    vint fib(n+1, 1);
    for(int i=2; i<n+1; i++){
        fib[i] = fib[i-1] + fib[i-2];
    }
    cout << fib[n] << endl;
}