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<iostream>
#include<string>
#include<vector>
#include<algorithm>
#include<map>
#include<set>
#include<cstdio>
#include<cmath>
#include<deque>
#include<numeric>
#include<queue>
#include<stack>
#include<cstring>
#include<limits>
#include<functional>
#include<unordered_set>
#include<iomanip>
#include<cassert>
#include<regex>
#include<bitset>
#include<complex>
#include<chrono>
#include<random>
#define rep(i,a) for(int i=(int)0;i<(int)a;++i)
#define rrep(i,a) for(int i=(int)a-1;i>=0;--i)
#define REP(i,a,b) for(int i=(int)a;i<(int)b;++i)
#define RREP(i,a,b) for(int i=(int)a-1;i>=b;--i)
#define pb push_back
#define eb emplace_back
#define all(x) x.begin(),x.end()
using ll=long long;
constexpr ll mod = 1e9 + 7;
constexpr ll INF = 1LL << 60;

ll gcd(ll n, ll m) {
	ll tmp;
	while (m!=0) {
		tmp = n % m;
		n = m;
		m = tmp;
	}
	return n;
}

ll lcm(ll n, ll m) {
	return abs(n) / gcd(n, m)*abs(m);//gl=xy
}
 
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;
}
 
using namespace std;

ll dp[50];
void solve(){
  int n;
  cin>>n;
  memset(dp,0,sizeof(dp));
  dp[0]=1,dp[1]=1;
  rep(i,n-1)dp[i+2]=dp[i+1]+dp[i];
  cout<<dp[n]<<"\n";
}

int main(){
	ios::sync_with_stdio(false);
  cin.tie(0);
	cout<<fixed<<setprecision(15);
  solve();
	return 0;
}

C++: #include<iostream>
using namespace std;
#define max 44

int main()
{
	int n; cin >> n;
	int f[max];
	f[0] = 1;
	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<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;
 
// #define int long long
 
/* short */
#define pb push_back
#define print(x) cout << x << '\n'
 
/* REPmacro */
#define REP(i, n) for (int i = 0; i < (n); i++)
#define REPS(i, a, n) for (int i = (a); i < (n); i++)
 
/* typedef */
typedef long long ll;
typedef unsigned long long ull;
typedef vector<int> vi;
typedef vector<vector<int> > vii;
typedef pair<int, int> pii;

/* const */
const int INF = INT_MAX;
const int dx[] = {0, 1, 0, -1}, dy[] = {1, 0, -1, 0};

/* func */
inline bool is_uruu(int y) {return (y % 4 == 0 && (y % 100 != 0 || y % 400 == 0));}

int dp[45];

int fibo(int n)
{
  if (dp[n] != -1){
    return (dp[n]);
  }

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

signed main()
{
  ios::sync_with_stdio(false);
  int n;
  cin >> n;
  fill(dp, dp + 45, -1);
  print(fibo(n));
  return (0);
}

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

#define REP(i, n) for(int i=0;i<(int)(n);i++)
#define ALL(x) (x).begin(),(x).end()
const int INF = 1e9;

using namespace std;
int calc[45];

int fib(int n){
    if(calc[n] != 0)
        return calc[n];
    for(int i = 2; i <= n; i++)
        calc[i] = calc[i-2] + calc[i-1];
    return calc[n];
}

int main() {
    int n;
    cin >> n;
    REP(i, 45) calc[i] = 0;
    calc[0] = 1;
    calc[1] = 1;
    cout << fib(n) << endl;
    return 0;
}

C++: import std.algorithm;
import std.array;
import std.conv;
import std.math;
import std.range;
import std.stdio;
import std.string;
import std.typecons;

T read(T)() { return readln.chomp.to!T; }
T[] reads(T)() { return readln.split.to!(T[]); }
alias readint = read!int;
alias readints = reads!int;

/// n 番目のフィボナッチ数を求める
/// F(0) = 0, F(1] = 1, F(2) = 1, F(3) = 2, F(4) = 3
int fib(int n) {
    if (n == 0) return 0;

    auto mat = new Mat2x2([[1, 1], [1, 0]]);
    auto m = mat.pow(n, int.max);
    return m.get(0, 1);
}

void main() {
    int n = readint;
    // 問題文の定義だとF(0) = 1, F(1) = 1 なので値を 1 だけずらす
    writeln(fib(n + 1));
}

class Mat2x2 {
    private const N = 2;
    private const int[][] _mat;

    this(const int[][] init) {
        assert(init.length == N);
        assert(init[0].length == init[1].length && init[0].length == N);

        _mat = init.dup;
    }

    int get(int r, int c) const {
        return _mat[r][c];
    }

    Mat2x2 mul(const Mat2x2 m, int mod) const {
        auto t = new int[][](N, N);

        for (int i = 0; i < N; i++) {
            for (int j = 0; j < N; j++) {
                int x = 0;
                for (int k = 0; k < N; k++) {
                    x = (x + (_mat[i][k] * m.get(k, j)) % mod) % mod;
                }
                t[i][j] = x;
            }
        }
        return new Mat2x2(t);
    }

    Mat2x2 copy() const {
        return new Mat2x2(_mat);
    }

    Mat2x2 pow(int k, int mod) const {
        assert(k > 0);
        if (k == 1) return this.copy();

        auto m = this.pow(k / 2, mod);
        return k % 2 == 0
            ? m.mul(m, mod)
            : this.mul(m.mul(m, mod), mod);
    }

    void dump() const {
        writeln(_mat[0][0], " ", _mat[0][1]);
        writeln(_mat[1][0], " ", _mat[1][1]);
    }
}

C++: #include <iostream>

using namespace std;


int F[44];

int main() {
  F[0] = 1;
  F[1] = 1;
  for (int i = 2; i < 44; ++i) {
    F[i] = F[i-1] + F[i-2];
  }

  int input;
  cin >> input;
  cout << F[input]<< endl;
}