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 <cassert>
//PXjUXeZStdX
#include <cctype>
#include <cerrno>
#include <cfloat>
#include <ciso646>
#include <climits>
#include <clocale>
#include <cmath>
#include <csetjmp>
#include <csignal>
#include <cstdarg>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <ccomplex>
#include <cfenv>
#include <cinttypes>
#include <cstdbool>
#include <cstdint>
#include <ctgmath>
#include <cwchar>
#include <cwctype>

// C++
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>
#include <array>
#include <atomic>
#include <chrono>
#include <condition_variable>
#include <forward_list>
#include <future>
#include <initializer_list>
#include <mutex>
#include <random>
#include <ratio>
#include <regex>
#include <scoped_allocator>
#include <system_error>
#include <thread>
#include <tuple>
#include <typeindex>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
// #include <boost/foreach.hpp>
// #include <boost/range/algorithm.hpp>
#define rep(i,j,k) for(int i=(int)j;i<(int)k;i++)
#define ll long long
#define Sort(v) sort(all(v))
//#define INF 1e9
#define LINF (1LL<<40)
#define END return 0
#define pb push_back
#define se second
#define fi first
#define pb push_back
#define all(v) (v).begin() , (v).end()
#define MP make_pair
#define int long long
using namespace std;
int day[12]={31,28,31,30,31,30,31,31,30,31,30,31};
// int dx[]={0,1,0,-1};
// int dy[]={1,0,-1,0};
typedef pair<int,int> P;

const long long MOD=1000000007LL;
bool isupper(char c){if('A'<=c&&c<='Z')return 1;return 0;}
bool islower(char c){if('a'<=c&&c<='z')return 1;return 0;}
bool iskaibun(string s){for(int i=0;i<s.size()/2;i++)if(s[i]!=s[s.size()-i-1])return 0;return 1;}
bool isnumber(char c){return ('0'<=c&&c<='9');}
bool isalpha(char c){return (isupper(c)||islower(c));}
template<typename T> 
void print(vector<T> v){
    for(int i=0;i<v.size();i++){
        if(i)cout<<" ";
        cout<<v[i];
    }
    cout<<endl;
}
int INF=1e18;

template<typename T>
void printendl(vector<T> v){
    for(auto date:v)cout<<date<<endl;
}

template<typename T>
void printvv(vector<vector<T>> v){
    for(int i=0;i<v.size();i++){
        for(int j=0;j<v[i].size();j++){
            if(j)cout<<" ";
            cout<<v[i][j];
        }
        cout<<endl;
    }
}
int gcd(int a,int b){
    if(a<b)swap(a,b);
    if(b==0)return a;
    else return gcd(b,a%b);
}

int powl(int n,int p){
    int ret=1;
    for(int i=0;i<p;i++)ret*=n;
    return ret;
}

struct Edge{
    int to,cost;
};

struct S{
    pair<int,int> p;
    int x;
};

signed main (){
    int n;
    cin>>n;
    int v[50];
    v[1]=v[0]=1;
    rep(i,2,50){
        v[i]=v[i-1]+v[i-2];
    }
    cout<<v[n]<<endl;


    
    


}

/*
4/N-1/h-1/n=1/w
4hn-Nn-Nh/hnN=1/w


*/

C++: #include<iostream>
#include<string>
#include<string.h>
#include<algorithm>
#include<stdio.h>
#include<cmath>
#include<vector>
#include<utility>
#include<stack>
#include<queue>
#include<list>
#include<bitset>
#include<functional>

#define FOR(i, a, b) for(long long int i=(a);i<=(b);i++)
#define RFOR(i, a, b) for(long long int i=(a);i>=(b);i--)
#define MOD 1000000007
#define INF 1000000000 //2000000000
#define LLINF 1000000000000000000 //9000000000000000000
#define PI 3.14159265358979

using namespace std;
typedef long long int ll;
typedef pair<long long int, long long int> P;

int main(void) {
	ll dp[45];
	int n;

	dp[0] = dp[1] = 1;

	cin >> n;

	FOR(i, 2, n) {
		dp[i] = dp[i - 1] + dp[i - 2];
	}
	cout << dp[n] << endl;
	
	return 0;
}

C++: #include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

//??\???
#define MAX_N 44
int dp[MAX_N + 1];

int main() {
  ios::sync_with_stdio(false);
  int n;
  cin >> n;
  dp[0] = 1;
  dp[1] = 1;
  for(int i = 2; i <= n; i++) {
    dp[i] = dp[i-1] + dp[i-2];
  }

  cout << dp[n] << "\n";

  return 0;
}

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

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

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

C++: #include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <string>
#include <cmath>
using namespace std;
#define MOD 1000000007
#define INF 1<<30
#define LINF (ll)1<<62
#define MAX 510000
#define rep(i,n) for(ll i=0; i<(n); i++)
#define REP(i,a,b) for(ll i=(a); i<(b); i++)
#define all(x) (x).begin(),(x).end()
#define uni(q) unique(all(q)),q.end()
using namespace std;
typedef long long ll;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef pair<ll, ll> P;
typedef vector<pair<ll, ll>> vpl;

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

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


void fibonacci(int n){
  vector<int> fib;

  fib.push_back(1);
  fib.push_back(1);

  if(n < 2){
    cout << "1" << endl;
  }else if(n == 2){
    fib.push_back(fib.at(0) + fib.at(1));
    cout << fib.back() << endl;
  }else{
    for(int i = 2;i < n+1;i++){
      fib.push_back(fib.at(i - 2) + fib.at(i - 1));
      cout << fib.back() << endl;
    }
  }

}

int main(){
  int n;
  cin >> n;
  fibonacci(n);

  return 0;
}

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

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

C++: #include <stdio.h>

#define MAX_N (50)

int memo[MAX_N];

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

    memo[0] = memo[1] = 1;

    for ( int i = 2; i <= n; i++ ) {
    	memo[i] = memo[i-1] + memo[i-2];
    }
    printf("%d\n", memo[n]);

    return 0;
}