Go: package main

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

// I/O
type Scanner struct {
	sc *bufio.Scanner
}

func NewScanner() *Scanner {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	sc.Buffer(make([]byte, 1024), int(1e+9))
	return &Scanner{sc}
}

func (s *Scanner) nextStr() string {
	s.sc.Scan()
	return s.sc.Text()
}

func (s *Scanner) nextInt() int {
	i, e := strconv.Atoi(s.nextStr())
	if e != nil {
		panic(e)
	}
	return i
}

func (s *Scanner) nextFloat() float64 {
	f, e := strconv.ParseFloat(s.nextStr(), 64)
	if e != nil {
		panic(e)
	}
	return f
}

func (s *Scanner) nextRuneSlice() []rune {
	return []rune(s.nextStr())
}

func (s *Scanner) nextIntSlice(n int) []int {
	res := make([]int, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextInt()
	}
	return res
}

func (s *Scanner) nextFloatSlice(n int) []float64 {
	res := make([]float64, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextFloat()
	}
	return res
}

// Arithmetic
func max(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m < i {
			m = i
		}
	}
	return m
}

func min(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m > i {
			m = i
		}
	}
	return m
}

func abs(x int) int {
	if x > 0 {
		return x
	}
	return -x
}

func pow(x, y int) int {
	res := 1
	for i := 0; i < y; i++ {
		res *= x
	}
	return res
}

func ceil(a, b int) int {
	if a%b == 0 {
		return a / b
	} else {
		return a/b + 1
	}
}

// Sort
type RuneSlice []rune

func (a RuneSlice) Len() int           { return len(a) }
func (a RuneSlice) Less(i, j int) bool { return a[i] < a[j] }
func (a RuneSlice) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }

// Main
func main() {
	sc := NewScanner()
	wtr := bufio.NewWriter(os.Stdout)
	N := sc.nextInt()
	dp := make([]int, N+1)
	dp[0] = 1
	dp[1] = 1
	for i := 2; i <= N; i++ {
		dp[i] = dp[i-1] + dp[i-2]
	}

	fmt.Fprintln(wtr, dp[N])
	wtr.Flush()
}

C++: #include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i=0;i<n;i++)
#define REP(i,s,n) for(int i=s;i<n;i++)
#define all(a) a.begin(),a.end()
typedef long long ll;
const double phi = (1 + sqrt(5)) / 2;
const double phi_ = (1 - sqrt(5)) / 2;
double fib(ll n){
    double res = pow(phi, n+1) - pow(phi_, n+1);
    return res / sqrt(5);
}
int main(){
    ll n, ans; cin >> n;
    ans = fib(n);
    cout << ans << 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] << endl;
    
    return 0;
}

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

using namespace std;

int F[50];

int fib(int n) {

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

	F[n] = fib(n - 1) + fib(n - 2);

	return F[n];
}

int main() {

	int n;
	scanf("%d", &n);

	for (int i = 0; i < n; ++i) {
		F[i] = 0;
	}

	cout << fib(n) << endl;

	return 0;

}

C++: #include "stdio.h"

#define MAX 50
#define INIT -1

int dp[MAX];

int fibonacci(int n){
  if(n == 0 || n == 1){
    return dp[n] = 1;
  }

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


int main(void){
  
  int N;
  scanf("%d", &N);
  
  for(int i=0;i<MAX;i++){
    dp[i] = INIT;
  }
    
  printf("%d\n", fibonacci(N));

  return 0;
}

C++: #line 1 "/mnt/c/Users/leafc/dev/compro/lib/template.hpp"


#include <bits/stdc++.h>
#define REP(i, n) for (int i = 0; i < n; i++)
#define FOR(i, m, n) for (int i = m; i < n; i++)
#define ALL(v) (v).begin(), (v).end()
#define coutd(n) cout << fixed << setprecision(n)
#define ll long long int
#define vl vector<ll>
#define vi vector<int>
const int INF = 2147483647;
const ll MOD = 1000000007;

using namespace std;


#line 2 "tmp.cpp"

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

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

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

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