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 <iostream>

#define rep(i, n) for (int i = 0; i < (int)(n); ++i)

const int SIZE = 45;
int f[SIZE];

int fib(int n) {
  if (f[n]) return f[n];

  if (n == 0 || n == 1) return f[n] = 1;
  return f[n] = fib(n - 1) + fib(n - 2);
}

int main() {
  int n;
  std::cin >> n;

  std::cout << fib(n) << '\n';
  return 0;
}

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

using namespace std;

#define FOR(i, j, k) for(int i = j; i < k; ++i)
#define rep(i, j) FOR(i, 0, j)
#define repr(i, j) for(int i = j; i >= 0; --i)
#define INF (1 << 30)
#define MOD 1e9 + 7

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> P;

int dp[45];

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

int main() {
	memset(dp, -1, sizeof(dp));
	dp[0] = 1;
	dp[1] = 1;
	int n;
	scanf("%d", &n);
	printf("%d\n", fib(n));
	return 0;
}

C++: #define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
using namespace std;
template<typename T> bool chmax(T &a,T b){if(a<b){a=b;return true;}return false;}
template<typename T> bool chmin(T &a,T b){if(a>b){a=b;return true;}return false;}
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define all(vec) vec.begin(),vec.end()
typedef long long ll;
typedef pair<ll,ll> pll;
typedef pair<int,int> pii;
typedef tuple<ll,ll,ll> tlll;
typedef tuple<int,int,int> tiii;
const ll mod=1e9+7;
const int inf=1<<30;

ll dp[45];

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

C++: #include<cstdio>
#include<cmath>
#include<algorithm>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<cstdlib>
#include<iomanip>
#include<queue>
#include<set>
#include <valarray>
#include<stack>
#include<sstream>
#include<math.h>

using namespace std;

void Solution()
{
	int n;
    cin >> n;
    
    vector<int> a;
    a.push_back(0);
    a[0]=1;
    
    a.push_back(1);
    a[1]=1;
    
    for ( int i = 2; i <= n; i++ ) 
    {
        a.push_back(i);
        a[i] = a[i-2] + a[i-1];
    }
    
    cout << a[n] << endl;
}

int main()
{
	Solution();
	return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
int  F[45]={};
int fib(int n){
  if(n==0||n==1)return 1;
  if(F[n]!=0)return F[n];
  return F[n]=fib(n-1)+fib(n-2);
}

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

C++: // C++ 14
#include <iostream>
#include <string>
#include <vector>
#include <list>
#include <algorithm>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <unordered_map>
#include <math.h>

#define ll long long
#define Int ll
#define loop(__x, __start, __end) for(Int __x = __start; __x < __end; __x++)
#define loopdown(__x, __start, __end) for(Int __x = __start; __x > __end; __x--)
#define rep(__n) for(Int __x = 0; __x < __n; __x++)
#define span(__a,__x,__y) __a.begin()+__x,__a.begin()+__y
#define span_all(__a) __a.begin(),__a.end()
#define len(__x) (__x.size())
#define last(__x) (__x[__x.size()-1])

using namespace std;

struct Point {
  Int x, y;
  Point(Int x, Int y): x(x), y(y) {}
  Point(): x(0), y(0) {}

  bool operator< (const Point &p1) const {
    return x < p1.x && y < p1.y;
  }
};
ostream & operator << (ostream & out, Point const & v) {
  out << "Point(" << v.x << ", " << v.y << ')';
  return out;
}

istream & operator >> (istream & in, Point & v) {
  Int x, y;
  in >> x; in >> y; v.x = x; v.y = y;
  return in;
}

// Geometry

#define EPS 0.0000000001

class Vector2 {
public:
  double x, y;
  
  Vector2(double x = 0, double y = 0): x(x), y(y) {}
  
  Vector2 operator + (Vector2 v) { return Vector2(x + v.x, y + v.y); }
  Vector2 operator - (Vector2 v) { return Vector2(x - v.x, y - v.y); }
  Vector2 operator * (double k) { return Vector2(x * k, y * k); }
  Vector2 operator / (double k) { return Vector2(x / k, y / k); }
  
  double length() { return sqrt(norm()); }
  double norm() { return x * x + y * y; }
  double dot (Vector2 v) { return x * v.x + y * v.y; }
  double cross (Vector2 v) { return x * v.y - y * v.x; }
  
  bool operator < (const Vector2 &v) const {
    return x != v.x ? x < v.x : y < v.y;
  }
  
  bool operator == (const Vector2 &v) const {
    return fabs(x - v.x) < EPS && fabs(y - v.y) < EPS;
  }
};

ostream & operator << (ostream & out, Vector2 const & v) { 
  out<< "Vector2(" << v.x << ", " << v.y << ')';
  return out;
}

istream & operator >> (istream & in, Vector2 & v) { 
  double x, y;
  in >> x;
  in >> y;
  v.x = x;
  v.y = y;
  return in;
}

Int N;

void input() {
  cin >> N;
}

vector<Int> dp(45, -1);

Int fib(Int n) {
  if (~dp.at(n)) return dp.at(n);
  Int m = fib(n-1) + fib(n-2);
  dp.at(n) = m;
  return m;
}

void solve() {
  dp.at(0) = dp.at(1) = 1;
  cout << fib(N) << endl;
}

int main() {
  input();
  solve();
  return 0;
}

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

int fib(int n)
{
	int f[45]={0};
	if(n==0 || n==1) return f[n]=1;
	if(f[n]>0) 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++: #include <bits/stdc++.h>
using namespace std;

int memo[50];

int fib(int n){
	  if(memo[n] != -1)
			return memo[n];
	  
	  if(n==0 or n==1){
			memo[n] = 1;
			return 1;
	  }
	  int ans = fib(n-1) + fib(n-2);
	  memo[n] = ans;
	  return ans;
}

int main (){

	  int n;
	  cin >> n;
	  memset(memo,-1,sizeof(memo));
	  cout << fib(n) << endl;

}

C++: #include <iostream>
#include <algorithm>
#include <vector>
#define debug(x) cout << #x << "==" << x << endl;

using namespace std;

//??\???
#define MAX_N 44
int N;
int dp[MAX_N];

int main() {
  ios::sync_with_stdio(false);

  cin >> N;

  // dp[0] = dp[1] = 1;
  // for(int i = 2; i <= N; i++) {
  //   dp[i] = dp[i-1] + dp[i-2];
  // }

  int now = 1;
  int prev1 = 1, prev2 = 1;
  for(int i = 2; i <= N; i++) {
    now = prev1 + prev2;
    prev2 = prev1;
    prev1 = now;
  }

  cout << now << endl;

  return 0;
}