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"
using namespace std;
typedef long long ll;
// #define int long long

template <class T>
bool INRANGE(T x, T a, T b) { return a <= x && x <= b; }
template <class T>
inline bool chmin(T &a, T b)
{
    if (a > b)
    {
        a = b;
        return true;
    }
    return false;
}
template <class T>
inline bool chmax(T &a, T b)
{
    if (a < b)
    {
        a = b;
        return true;
    }
    return false;
}

#define REP(i, n) for (int i = 0; i < (n); ++i)
#define RREP(i, n) for (int i = (n); i >= 0; --i)
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define RFOR(i, a, b) for (int i = (a); i >= (b); --i)
#define ALL(v) (v).begin(), (v).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" \
                      << " " << __FILE__ << endl;

typedef vector<int> vi;
typedef vector<string> vs;
typedef vector<vi> vvi;
typedef pair<int, int> pii;

vi dp(100, -1);

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

int main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);

    int n;
    cin >> n;
    cout << fib(n) << endl;

    return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
#define int long long
int memo[50];
int fib(int n){
  if(~memo[n]) return memo[n];
  if(n<=1) return 1;
  return memo[n]=(fib(n-1)+fib(n-2));
}
signed main(){
  int n;
  cin>>n;
  memset(memo,-1,sizeof(memo));
  cout<<fib(n)<<endl;
  return 0;
}

C++: #include "bits/stdc++.h"
#define rep(i,n) for(int i = 0; i < (n); ++i)
using namespace std;
/*
using ll = long long;
using P = pair<int, int>;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
*/
int fib[50];

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n;
    cin >> n;
    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;
    return 0;
}

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


int main() {
	int n;
	int F[10000];
	cin >> n;

	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 "bits/stdc++.h"
#pragma GCC optimize("Ofast")

// Begin Header {{{
using namespace std;

#ifndef DEBUG
#define dump(...)
#endif

#define all(x) x.begin(), x.end()
#define rep(i, b, e) for (intmax_t i = (b), i##_limit = (e); i < i##_limit; ++i)
#define reps(i, b, e) for (intmax_t i = (b), i##_limit = (e); i <= i##_limit; ++i)
#define repr(i, b, e) for (intmax_t i = (b), i##_limit = (e); i >= i##_limit; --i)
#define var(Type, ...) Type __VA_ARGS__; input(__VA_ARGS__)

constexpr size_t    operator""_zu(unsigned long long value) { return value; };
constexpr intmax_t  operator""_jd(unsigned long long value) { return value; };
constexpr uintmax_t operator""_ju(unsigned long long value) { return value; };

constexpr int INF = 0x3f3f3f3f;
constexpr intmax_t LINF = 0x3f3f3f3f3f3f3f3f_jd;

template <class T, class Compare = less<>>
using MaxHeap = priority_queue<T, vector<T>, Compare>;
template <class T, class Compare = greater<>>
using MinHeap = priority_queue<T, vector<T>, Compare>;

inline void input() {}
template <class Head, class... Tail>
inline void input(Head&& head, Tail&&... tail) {
    cin >> head;
    input(forward<Tail>(tail)...);
}

template <class T>
inline istream& operator>>(istream &is, vector<T> &vec) {
    for (auto &e: vec) {
        is >> e;
    }
    return is;
}

inline void output() { cout << "\n"; }
template <class Head, class... Tail>
inline void output(Head&& head, Tail&&... tail) {
    cout << head;
    if (sizeof...(tail)) {
        cout << " ";
    }
    output(forward<Tail>(tail)...);
}

template <class T>
inline ostream& operator<<(ostream &os, const vector<T> &vec) {
    static constexpr const char *delim[] = {" ", ""};
    for (const auto &e: vec) {
        os << e << delim[&e == &vec.back()];
    }
    return os;
}

template <class T>
inline vector<T> makeVector(const T &initValue, size_t sz) {
    return vector<T>(sz, initValue);
}

template <class T, class... Args>
inline auto makeVector(const T &initValue, size_t sz, Args... args) {
    return vector<decltype(makeVector<T>(initValue, args...))>(sz, makeVector<T>(initValue, args...));
}

template <class Func>
class FixPoint : Func {
public:
    explicit constexpr FixPoint(Func&& f) noexcept : Func(forward<Func>(f)) {}

    template <class... Args>
    constexpr decltype(auto) operator()(Args&&... args) const {
        return Func::operator()(*this, std::forward<Args>(args)...);
    }
};

template <class Func>
static inline constexpr decltype(auto) makeFixPoint(Func&& f) noexcept {
    return FixPoint<Func>{forward<Func>(f)};
}

template <class Container>
struct reverse_t {
    Container &c;
    reverse_t(Container &c) : c(c) {}
    auto begin() { return c.rbegin(); }
    auto end() { return c.rend(); }
};

template <class Container>
auto reversed(Container &c) {
    return reverse_t<Container>(c);
}

template <class T>
inline bool chmax(T &a, const T &b) noexcept {
    return b > a && (a = b, true);
}

template <class T>
inline bool chmin(T &a, const T &b) noexcept {
    return b < a && (a = b, true);
}

template <class T>
inline T diff(const T &a, const T &b) noexcept {
    return a < b ? b - a : a - b;
}
// End Header }}}

signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.setf(ios_base::fixed);
    cout.precision(10);

    var(size_t, n);

    vector<intmax_t> fib(n + 1);
    fib[0] = fib[1] = 1;
    reps(i, 2, n) fib[i] = fib[i - 1] + fib[i - 2];

    output(fib[n]);

    return 0;
}

C++: #pragma GCC target("avx")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include<bits/stdc++.h>
using namespace std;
#define rep(i, n) for (long long i = 0; i < (long long)(n); i++)
using ll = long long;
using P = pair<ll,ll>;

int main(){
ios::sync_with_stdio(false);
std::cin.tie(nullptr);
ll dp[45];
dp[0] = dp[1] = 1;
ll n;
cin >> n;
for(ll i = 2; i < 45; i++){
    dp[i] = dp[i - 1] + dp[i - 2];
}
cout << dp[n] << endl;
}

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

using namespace std;

int main() {
    int32_t n;
    cin >> n;

    vector<int32_t> fib(n+1);
    fib[0] = 1;
    fib[1] = 1;
    for (int32_t i = 2; i <= n; i++) {
        fib[i] = fib[i-1] + fib[i-2];
    }

    cout << fib[n] << endl;

    return 0;
}

C++: #include<iostream>
using namespace std;
int main() {
  int n;
  int dp[45] = {};
  cin >> n;
  dp[1] = 1;
  dp[0] = 1;

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