Go: package main

/*
フィボナッチ数列
*/

import (
	"bufio"
	"bytes"
	"fmt"
	"log"
	"os"
	"strconv"
	"strings"
)

func fibWithMemo(n int, memo map[int]int) int {
	if n == 0 || n == 1 {
		return 1
	}
	if val, ok := memo[n]; ok {
		return val
	}
	memo[n] = fibWithMemo(n-1, memo) + fibWithMemo(n-2, memo)
	return memo[n]
}

func fib(n int) int {
	memo := make(map[int]int)
	return fibWithMemo(n, memo)
}

func main() {
	scanner := makeScanner(1024)
	n := eGetInt(scanner)
	fmt.Println(fib(n))
}

////////////////////////////////////////////////////////////////////////////////
// ライブラリ
////////////////////////////////////////////////////////////////////////////////
func makeScanner(maxByte int) *bufio.Scanner {
	scanner := bufio.NewScanner(os.Stdin)
	scanner.Buffer(make([]uint8, 0, 8192), maxByte)
	return scanner
}
func makeWordScanner() *bufio.Scanner {
	scanner := makeScanner(8192)
	scanner.Split(bufio.ScanWords)
	return scanner
}
func eGetLine(r *bufio.Scanner) string {
	if r.Scan() {
		return r.Text()
	}
	err := r.Err()
	if err != nil {
		log.Fatal(err)
	}
	// EOF
	return ""
}
func eGetInt(r *bufio.Scanner) int {
	line := eGetLine(r)
	return eAtoi(line)
}
func eGetFields(r *bufio.Scanner) []string {
	line := eGetLine(r)
	return strings.Fields(line)
}
func eGetInts(r *bufio.Scanner) []int {
	fields := eGetFields(r)
	ints := make([]int, len(fields))
	for i := 0; i < len(ints); i++ {
		ints[i] = eAtoi(fields[i])
	}
	return ints
}
func eGetChars(r *bufio.Scanner) []string {
	line := eGetLine(r)
	return strings.Split(line, "")
}
func eAtoi(s string) int {
	n, err := strconv.Atoi(s)
	if err != nil {
		log.Fatal(err)
	}
	return n
}

type ints []int

func (s ints) String() string {
	var buf bytes.Buffer
	buf.WriteString("[")
	sep := ""
	for _, v := range s {
		buf.WriteString(fmt.Sprintf("%s%d", sep, v))
		sep = ", "
	}
	buf.WriteString("]")
	return buf.String()
}

func reverse(a ints) ints {
	r := make(ints, len(a))
	for i := 0; i < len(a); i++ {
		r[i] = a[len(a)-1-i]
	}
	return r
}
func max(a ints) (int, bool) {
	if len(a) == 0 {
		return 0, false
	}
	m := a[0]
	for _, e := range a {
		if e > m {
			m = e
		}
	}
	return m, true
}
func min(a []int) int {
	m := a[0]
	for _, v := range a {
		if v < m {
			m = v
		}
	}
	return m
}

func sum(a ints) int {
	if len(a) == 0 {
		return 0
	}
	sum := 0
	for _, e := range a {
		sum += e
	}
	return sum
}
func find(n int, a ints) int {
	for i, v := range a {
		if n == v {
			return i
		}
	}
	return -1
}

C++: #include <cstdio>
#define NMAX 45

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

    if (n == 0 || n == 1) {
        printf("1\n");
    } else {
        int fib[NMAX];
        fib[0] = fib[1] = 1;
        for (int i = 2; i < NMAX; i++) {
            fib[i] = fib[i-1] + fib[i-2];
            if (i == n) {
                printf("%d\n", fib[i]);
                break;
            }
        }
    }
    return 0;
}

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

int fib(int n);

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

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

C++: #include <iostream>
using ll = long long;
using namespace std;
#define MAX 50
/* initialize */
int fibs[MAX];

/* main */
int main() {

    int n;
    cin >> n;
    fibs[0]=fibs[1] = 1;
    for (int i = 2; i <= n; i++) {
        fibs[i] = fibs[i-1] + fibs[i-2];
    }
    cout << fibs[n] << "\n";
    return 0;
}

C++: #include <iostream>
#include <sys/time.h>
using namespace std;

int memo[100] = {0};

int fibo(int n){//メモ化再帰を用いて再計算を防ぎ、再帰計算速度を上げる
    if(memo[n] != 0) return memo[n];
    if(n == 0 || n == 1) return 1;
    memo[n] = fibo(n - 1) + fibo(n - 2);
    return memo[n];
}

int main(void){
    int n;
    cin >> n;
    fibo(n);
    cout <<  fibo(n) << endl;
}

C++: #include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int MAXN = 50;
int n;
ll f[MAXN];

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

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

using namespace std;
using ll = long long;
using v1 = vector<int>;
using vl = vector<long long>;
using v2 = vector<vector<int>>;
using v3 = vector<vector<char>>;

int n;

int fib(int x, int y, int i){
	if(i == n) return x+y;
	i++;
	fib(y, x+y, i);
}

int main(){
	cin >> n;
	if(n == 1 || n == 0){
		cout << 1 << endl;
		return 0;
	}
	cout << fib(1, 1, 2) << endl;
}

C++: #include <iostream>
using namespace std;
int main(){
  int n;
  long long int fib1,fib2,fib3;
  cin>>n;
  fib1=1;
  fib2=1;
  if(n==0){
    cout<<0<<endl;
  }else if(n==1){
    cout<<1<<endl;
  }else if(n>=2){
    for(int i=0;i<n-1;i++){
      fib3=fib1+fib2;
      fib1=fib2;
      fib2=fib3;
    }
    cout<<fib3<<endl;
  }
}

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

int main() {
  int n; cin >> n;
  int fib[50];
  fib[0] = fib[1] = 1; //初期条件
  //n>=2のとき
  for ( int i = 2; i <= n; i++ ) {
    fib[i] = fib[i-2] + fib[i-1];
  }

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

C++: #include "bits/stdc++.h"
#include "math.h"
 
using namespace std;
typedef long long ll;
typedef vector<ll> vll;
typedef vector<vll> vvll;
typedef vector<bool> vb;
typedef vector<vb> vvb;
typedef vector<int> vin;
typedef vector<vin> vvin;
typedef pair<ll,ll> P;
typedef vector<P> vp;
#define rep(i,a,b) for(ll i=(a);i<(b);++i)
#define drep(i,a,b) for(ll i=(a);i>=(b);--i)
#define SIZE(a) int((a).size())
const int MOD=1e9+7;

int main(){
  ll n;cin>>n;
  vll dp(n+1,1);
  rep(i,2,n+1){
    dp[i]=dp[i-2]+dp[i-1];
  }
  cout<<dp[n]<<endl;
}