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<algorithm>
#include<bitset>
#include<iostream>
#include<iomanip>
#include<set>
#include<string>
#include<math.h>
#include<string>
#include<queue>
#include<vector>
using namespace std;
typedef long long int ll;
typedef pair<int, ll> P;

//--------------
//#define DEBUG
//--------------

#ifdef DEBUG
	#define debugprint(x) cout<<x<<" "
	#define debugendl cout<<endl
	#define debug(x) x
#else
	#define debugprint(x)
	#define debugendl
	#define debug(x)
#endif

class zahyo{
	public:
	int x;
	int y;
	zahyo(){
		x=0;
		y=0;
	}
	zahyo(int x_,int y_){
		x=x_;
		y=y_;
	}
	void print(){
		cout<<x<<" "<<y;
	}
	zahyo operator+(zahyo add){
		add.x=this->x+add.x;
		add.y=this->y+add.y;
		return add;
	}
	zahyo operator-(zahyo add){
		add.x=this->x-add.x;
		add.y=this->y-add.y;
		return add;
	}
	zahyo operator*(int t){
		zahyo temp;
		temp.x=this->x*t;
		temp.y=this->y*t;
		return temp;
	}
	zahyo operator%(int t){
		zahyo temp(this->x%t,this->y%t);
		return temp;
	}
	zahyo operator/(int t){
		zahyo temp(this->x/t,this->y/t);
		return temp;
	}
	bool operator==(const zahyo add) const{
		if(add.x==this->x and add.y==this->y){return true;}
		else{return false;}
	}
	bool operator!=(const zahyo add) const{
		if(add.x==this->x or add.y==this->y){return false;}
		else{return true;}
	}
	bool operator<(const zahyo add) const{
		if(this->x<add.x){return true;}
		else if(this->x==add.x and this->y<add.y){return true;}
		else{return false;}
	}
	bool operator>(const zahyo add) const{
		if(this->x>add.x){return true;}
		else if(this->x==add.x and this->y>add.y){return true;}
		else{return false;}
	}
	void input(){
		cin>>x>>y;
	}
};

zahyo ways[4];

bool IsInBoard(int x,int maxx, int y,int maxy){
	if(x>=0 and x<maxx and y>=0 and y<maxy){
		return true;
	}
	else{
		return false;
	}
}

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

C++: #include <iostream>
#include <algorithm>
#include <string>
#include <string.h>
#include <stdlib.h>
#include <math.h>
#include <vector>
#include <queue>
#include <stack>
#include <cmath>
#include <map>
#include <iomanip>
#include <set>
#include <ctime>
#include <tuple>
#include <bitset>
using namespace std;

/*
sort(sp.begin(), sp.end(), [](PAIR l, PAIR r){
        return l.first<r.first || (l.first==r.first && l.second > r.second);
        });
*/

typedef long long  ll;

#define fi first
#define se second

using Graph = vector<vector<int>>;


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



    return 0;
}

C++: #include "bits/stdc++.h"
using namespace std;
typedef long long ll;
#define _USE_MATH_DEFINES
#include <math.h>
#define rep(i,n) for(int i = 0;i < n;i++)
#define NIL = -1;

ll gcd(long long a,long long b) {
    if (a < b) swap(a,b);
    if (b == 0) return a;
    
    return gcd(b,a%b);
}

ll lcm(ll a,ll b){
    a / gcd(a,b) * b;
}
const ll mod = 1e9 + 7;

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

const ll INF = 1e9;
/////////////////////////////////////////////////////////////////////////////////////////

int main(){
    int n;
    cin >> n;
    int dp[50];
    dp[0] = 1;
    dp[1] = 1;

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

    cout << dp[n] << endl;

}

C++: #include<iostream>
using namespace std;
int main ()
{
	int fif[100];
	int n,i;
	fif[0]=1,fif[1]=1;
	cin >> n;
	for(i=2;i<=n;i++)
	{
		fif[i]=fif[i-2]+fif[i-1];
	}
	cout << fif[n] << endl;
	return 0;
}

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

using namespace std;
typedef long long int ll;

int dh[4] = {1,0,-1,0};
int dw[4] = {0,1,0,-1};

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

C++: #include <algorithm>
#include <cmath>
#include <functional>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <vector>
using namespace std;
const int INT_INF = 500000000;
const long long LONG_LONG_INF = (long long)pow(10, 18);
const int MOD = pow(10, 9) + 7;
/* contest template */
int n;
long long fib[45];

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

C++: #include<bits/stdc++.h>
using namespace std;
int fibo(int n){
  if(n==0||n==1)return 1;
  return fibo(n-1)+fibo(n-2);
}
int main(){
  int n;
  cin >> n;
  cout << fibo(n) << endl;
  return 0;
}

C++: #include <cstdio>
#include <iostream>
#include <cmath>
#include <ctype.h>
#include <string>
#include <sstream>
#include <algorithm>
#include <cstdlib>
#include <map>
#include <queue>
#include <utility>
#include <vector>
#include <set>

using namespace std;

int main()
{
    int fib[45] = {};
    fib[0] = fib[1] = 1;

    int n;
    cin >> n;
    if (n < 2) {
        cout << fib[n];
    } else {
        for (int i = 2; i <= n; i++) {
            fib[i] = fib[i - 1] + fib[i - 2];
        }
        cout << fib[n];
    }

    return 0;
}

C++: #include <iostream>

using namespace std;

int fibo[45];

int fib(int n) {
	if (fibo[n]) return fibo[n];
	return fibo[n] = fib(n - 1) + fib(n - 2);
}

int main() {
	int n; cin >> n;
	fibo[0] = fibo[1] = 1;
	cout << fib(n) << endl;

	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
#define REP(i, n) for (int i = 0; i < (int)(n); i++)
typedef long long ll;
typedef pair<int, int> P;
ll dp[55];
int main() {
  int n;
  cin >> n;
  dp[0] = 1;
  dp[1] = 1;
  for (int i = 2; i < 50; i++) {
    dp[i] = dp[i - 1] + dp[i - 2];
  }
  cout << dp[n] << endl;
}

C++: //
//  main.cpp
//  fibonacci_number
//
//  Created by ???????????? on 2017/10/17.
//  Copyright ?? 2017 ????????????. All rights reserved.
//

#include <iostream>
#include <stdio.h>

using namespace std;

int main(int argc, const char * argv[]) {
    int n;
    scanf("%d", &n);
    int A[n];
    A[0]=A[1]=1;
    for(int i = 2; i <= n; i++ ){
        A[i] = A[i-2]+A[i-1];
    }
    cout << A[n] <<endl;;
    return 0;
}