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++: // https://ei1333.github.io/luzhiled/
// http://beet-aizu.hatenablog.com/entry/2017/01/04/113233
// http://www.prefield.com/algorithm/
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using vl = vector<ll>;
using vd = vector<ld>;
using vs = vector<string>;
using vb = vector<bool>;
using vvl = vector<vector<ll>>;
using vvd = vector<vector<ld>>;
using vvs = vector<vector<string>>;
using vvb = vector<vector<bool>>;
#define pb push_back
#define eb emplace_back
#define fi first
#define se second
template<class T> using vc = vector<T>;
template<class T> using vvc = vector<vector<T>>;
using Graph = vector<vector<ll>>;
const ll INF = 1LL << 60;
void init() {cin.tie(0);ios::sync_with_stdio(false);cout << fixed << setprecision(15);}
const ll tl= 1000000007;
#define REP(i, n) for (ll i = 0; i < n; i++)
#define REREP(i, n) for (ll i = n; i >= 0; i--)
#define FOR(i, a, n) for (ll i = a; i < n; i++)
#define REFOR(i, n, a) for (ll i = n; i >= a; i--)
#define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() ) //被り削除
#define debug cout << "line : " << __LINE__ << " debug" << endl;
#define ini(...) int __VA_ARGS__; in(__VA_ARGS__)
#define inl(...) long long __VA_ARGS__; in(__VA_ARGS__)
#define ind(...) long double __VA_ARGS__; in(__VA_ARGS__)
#define ins(...) string __VA_ARGS__; in(__VA_ARGS__)
#define inc(...) char __VA_ARGS__; in(__VA_ARGS__)
void in(){} template <typename T,class... U> void in(T &t,U &...u){ cin >> t; in(u...);}
void out(){cout << endl;} template <typename T,class... U> void out(const T &t,const U &...u){ cout << t; if(sizeof...(u)) cout << " "; out(u...);}
template<typename T>void die(T x){out(x); exit(0);}
#define in1(A) REP(i,A.size()) in(A[i]);
#define in2(A,B) REP(i,A.size()) in(A[i],B[i]);
#define in3(s,t,u) REP(i,sz(s)){in(s[i] , t[i] , u[i]);}
#define in4(s,t,u,v) REP(i,sz(s)){in(s[i] , t[i] , u[i] , v[i]);}
#define each(x,v) for(auto& x : v)
#define all(v) (v).begin(),(v).end()
#define sz(v) ((int)(v).size())
struct Point{ ld x,y; };
ld dist(Point a, Point b){return sqrt(abs(a.x-b.x)*abs(a.x-b.x)+abs(a.y-b.y)*abs(a.y-b.y));} // ２点間の距離 
ll gcd(ll a, ll b) { return b != 0 ? gcd(b, a % b) : a; }
ll lcm(ll a,ll b){ return a / gcd(a,b) * b;} 
ll fact(ll n){ if(n < 2) return 1; return (n * fact(n-1))%tl; } //階乗
inline ll updiv(ll a,ll b){ return (a + b - 1) / b; } //切り上げ
template<typename T,typename U>ll ceil(T a,U b){return (a + b - 1) / b;}
template <class A, class B> inline bool chmax(A &a, const B &b) { return b > a && (a = b, true); }
template <class A, class B> inline bool chmin(A &a, const B &b) { return b < a && (a = b, true); }
//-------------------------------------------------------------------------------------------------
int main(){
    init();
    inl(n);
    vl dp(n+1,0);
    dp[0]=1; dp[1]=1;
    FOR(i,2,n+1) dp[i]= dp[i-1]+dp[i-2];
    out(dp[n]);
}

C++: #include <bits/stdc++.h>
using namespace std;

#define MAX 44

int DP[MAX + 1];

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

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

C++: #include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cassert>
#include <string>
#include <cstring>
#include <vector>
#include <list>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <algorithm>

using namespace std;

// ---------------------
// repetition
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n) FOR(i,0,n)

// debug
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;

// ---------------------
#define INF 922337203685477580
typedef long long ll;

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

int main() {
  int X;
  cin >> X;

  cout << fib(X) << endl;
  return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
typedef long long ll;

int Fib(int i, vector<int>& fib)
{
	if (i == 0) return 1;
	if (i == 1) return 1;
	if (fib[i]) return fib[i];
	return fib[i] = Fib(i - 1, fib) + Fib(i - 2, fib);
}

int main()
{
	int n;
	cin >> n;
	vector<int> fib(n + 1);
	cout << Fib(n, fib) << endl;
}

C++: #include<cstdio>

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

C++: #include<iostream>
#define MAX_N 45
int F[MAX_N];

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

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

C++: #include <iostream>

int main()
{
    int n;
    std::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];
    }
    std::cout << F[n] << std::endl;
}

C++: #include<bits/stdc++.h>
using namespace std;

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

C++: #include <iostream>

using namespace std;

int A[128];
int fib(int n){
  A[0] =1;
  for(int i=1;i<n;++i){
    A[i] =A[i-1];
    if(i>1)A[i]+=A[i-2];
    if(i>2)A[i]+=A[i-3];
  }
  return A[n-1];

}

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

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

int main() {
	int n[100000], s, i;
	n[0] = 1;
	n[1] = 1;

	cin >> s;

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

	cout << n[s] << endl;

	return 0;
}

C++:   /*  HARD WORK FOREVER PAYS  */
#include<bits/stdc++.h>
#define turbo(){	\
	ios_base::sync_with_stdio(false); \
	cin.tie(NULL); \
}
using namespace std;
typedef long long ll;
int dp[100];
ll fib(ll n){
	if(n==1||n==0) return 1;
	if(dp[n]!=-1) return dp[n];
	return dp[n]=fib(n-1)+fib(n-2);
}
int main()
{
	turbo();
	ll n;
	cin>>n;
	memset(dp,-1,sizeof(dp));
	cout<<fib(n)<<endl;
	return 0;	
}

C++: 
#include<iostream>

using namespace std;

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

C++: #include <iostream>
using namespace std;int main(){int a=1,b=1,c;cin>>c;for(int i=c-1;i;--i){swap(a,b);a+=b;}cout<<a<<endl;}

C++: #include <iostream>

using namespace std;

int fib(int n);

int main() {
    int n;

    //??\???
    cin >> n;

    //??????
    cout << fib(n) << endl;

    return 0;
}

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

C++: #include<stdio.h>

int fib(int);

int main()
{
  int a,n;

  scanf("%d",&n);

  if(n == 0 || n == 1){
    printf("%d\n",1);
  }
  else {
    a = fib(3);
    printf("%d\n",a);
  }

  return 0;
}

int fib(int n){

  if(n==0 || n==1){
    return 1;
  }

  return (fib(n-1)+fib(n-2));
}