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 <bits/stdc++.h>
#define REP(i,n) for (int i = 0; i <(n); ++i)
#define REP2(i,x,n) for (int i = x; i <(n); ++i)
#define ALL(v) v.begin(), v.end()
#define RALL(v) v.rbegin(), v.rend()
using namespace std;
using ll = long long;
using P = pair<int,int>;
static const double PI = acos(-1);
static const int INF = 1e9+7;


/*
DP
フィボナッチ数列

*/

int main(){

  int n;
  cin >> n;
  int fib[n+1];
  fib[0] = 1;
  fib[1] = 1;
  REP2(i,2,n+1){
    fib[i] = fib[i-1] + fib[i-2];
  }

  cout << fib[n] << endl;
  return 0;
}

C++: #include<stdio.h>

int dp[50];

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

int main() {
  int n, i;
  for ( i = 0; i < 50; i++ ) dp[i] = -1;

  scanf("%d", &n);
  printf("%d\n", fib(n));

  return 0;
}

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

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

}

C++: #include <bits/stdc++.h>
using namespace std;
#define Rep(i, n) for (int i = 0; i < (int)(n); i++)
#define BitRep(i, n) for (int i = 0; i < (int)(1 << n); i++)
#define Sum(vec) accumulate(vec.begin(), vec.end(), 0)
#define Sort(vec) sort(vec.begin(), vec.end())
#define Reverse(vec) reverse(vec.begin(), vec.end())
#define Next_permutation(vec) next_permutation(vec.begin(), vec.end())

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 <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <cmath>
#define rep(i, n) for(int i = 0; i < n; i++)
#define REP(i, m, n) for(int i = m; i < n; i++)
typedef long long ll;
using namespace std;

int main() {
    int n ;
    cin >> n;
    int dp[50];
    for(int i = 0; i <= n; i++) dp[i] = 0;
    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;

    return 0;
}

C++: #include <bits/stdc++.h>
#define rep(i,n) for (int i = (0); i < (n); ++i)
#define rrep(i,n) for(int i = 1; i <= (n); ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
#define limit(x,l,r) max(l,min(x,r))
#define lims(x,l,r) (x = max(l,min(x,r)))
#define isin(x,l,r) ((l) <= (x) && (x) < (r))
#define show(x) cout << #x << " = " << (x) << endl
#define show2(x,y) cout << #x << " = " << (x) << ", " << #y << " = " << (y) << endl
#define show3(x,y,z) cout << #x << " = " << (x) << ", " << #y << " = " << (y) <<  ", " << #z << " = " << (z) << endl
#define showv(v) rep(i,v.size()) printf("%d%c", v[i], i==v.size()-1?'\n':' ')
#define showv2(v) rep(j,v.size()) showv(v[j])
#define showt(t,n) rep(i,n) printf("%d%c", t[i], i==n-1?'\n':' ')
#define showt2(t,r,c) rep(j,r) showt(t[j],c)
#define showvp(p) rep(i,p.size()) printf("%d %d\n", p[i].first, p[i].second)
#define printv(v) rep(i,v.size()) printf("%d\n", v[i])
#define printt(t,n) rep(i,n) printf("%d\n", t[i])
#define incl(v,x) (find(all(v),x)!=v.end())
#define incls(s,c) (s.find(c)!=string::npos)
#define lb(a,x) distance((a).begin(),lower_bound(all(a),(x)))
#define ub(a,x) distance((a).begin(),upper_bound(all(a),(x)))
#define fi first
#define se second
#define pb push_back
#define eb emplace_back
#define sz(x) (int)(x).size()
#define pcnt __builtin_popcountll
#define bit(n,k) ((n>>k)&1) // nのk bit目
#define bn(x) ((1<<x)-1)
#define dup(x,y) (((x)+(y)-1)/(y))
#define newline puts("")
#define uni(x) x.erase(unique(all(x)),x.end())
#define SP << " " <<
#define v(T) vector<T>
#define vv(T) v(v(T))
using namespace std;
using ll = long long;
using ld = long double;
using vi = vector<int>;
using vvi = vector<vi>;
using vl = vector<ll>;
using vvl = vector<vl>;
using vs = vector<string>;
using P = pair<int, int>;
using T = tuple<int, int, int>;
using vp = vector<P>;
using vt = vector<T>;
const int mod = 1000000007;
const double EPS = 1e-9;
//const long double EPS = 1e-14;
const int INF = (1<<30)-1;
const ll LINF = (1LL<<62)-1;
#define dame { puts("No"); return 0;}
#define yn {puts("Yes");}else{puts("No");}
inline int in() { int x; cin >> x; return x;}
inline ll lin() { ll x; cin >> x; return x;}
inline char chin() { char x; cin >> x; return x;}
inline string stin() { string x; cin >> x; return x;}
inline double din() { double x; cin >> x; return x;}
//template<class T = int> inline T in() { T x; cin >> x; return (x);}
template<typename T>inline ll suma(const v(T)& a) { ll res(0); for (auto&& x : a) res += x; return res;}
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }
char itoa(int n) { return n + '0';}
ll gcd(ll a, ll b) { return b?gcd(b,a%b):a;}
ll lcm(ll a, ll b) { return a/gcd(a,b)*b;}

int main () {
  int n = in();
  vi dp(n+1);
  dp[0] = dp[1] = 1;
  srep(i,2,n+1) dp[i] = dp[i-1] + dp[i-2];
  cout << dp[n] << endl;
  return 0;
}

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

std::vector<int> dp(50, 1);

int fibonacci(int n) {
  if (n < 2)
    return dp.at(n);
  if (dp.at(n) == 1)
    dp.at(n) = fibonacci(n-1) + fibonacci(n-2);
  return dp.at(n);
}

int main() {
  int n;
  std::cin >> n;
  std::cout << fibonacci(n) << std::endl;
}

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

#define N 45

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