Go: package main

/*
フィボナッチ数列
*/

import (
	"bufio"
	"bytes"
	"fmt"
	"log"
	"os"
	"strconv"
	"strings"
)

func fibWithMemo(n int, memo map[int]int) int {
	if n == 0 || n == 1 {
		return 1
	}
	if val, ok := memo[n]; ok {
		return val
	}
	memo[n] = fibWithMemo(n-1, memo) + fibWithMemo(n-2, memo)
	return memo[n]
}

func fib(n int) int {
	memo := make(map[int]int)
	return fibWithMemo(n, memo)
}

func main() {
	scanner := makeScanner(1024)
	n := eGetInt(scanner)
	fmt.Println(fib(n))
}

////////////////////////////////////////////////////////////////////////////////
// ライブラリ
////////////////////////////////////////////////////////////////////////////////
func makeScanner(maxByte int) *bufio.Scanner {
	scanner := bufio.NewScanner(os.Stdin)
	scanner.Buffer(make([]uint8, 0, 8192), maxByte)
	return scanner
}
func makeWordScanner() *bufio.Scanner {
	scanner := makeScanner(8192)
	scanner.Split(bufio.ScanWords)
	return scanner
}
func eGetLine(r *bufio.Scanner) string {
	if r.Scan() {
		return r.Text()
	}
	err := r.Err()
	if err != nil {
		log.Fatal(err)
	}
	// EOF
	return ""
}
func eGetInt(r *bufio.Scanner) int {
	line := eGetLine(r)
	return eAtoi(line)
}
func eGetFields(r *bufio.Scanner) []string {
	line := eGetLine(r)
	return strings.Fields(line)
}
func eGetInts(r *bufio.Scanner) []int {
	fields := eGetFields(r)
	ints := make([]int, len(fields))
	for i := 0; i < len(ints); i++ {
		ints[i] = eAtoi(fields[i])
	}
	return ints
}
func eGetChars(r *bufio.Scanner) []string {
	line := eGetLine(r)
	return strings.Split(line, "")
}
func eAtoi(s string) int {
	n, err := strconv.Atoi(s)
	if err != nil {
		log.Fatal(err)
	}
	return n
}

type ints []int

func (s ints) String() string {
	var buf bytes.Buffer
	buf.WriteString("[")
	sep := ""
	for _, v := range s {
		buf.WriteString(fmt.Sprintf("%s%d", sep, v))
		sep = ", "
	}
	buf.WriteString("]")
	return buf.String()
}

func reverse(a ints) ints {
	r := make(ints, len(a))
	for i := 0; i < len(a); i++ {
		r[i] = a[len(a)-1-i]
	}
	return r
}
func max(a ints) (int, bool) {
	if len(a) == 0 {
		return 0, false
	}
	m := a[0]
	for _, e := range a {
		if e > m {
			m = e
		}
	}
	return m, true
}
func min(a []int) int {
	m := a[0]
	for _, v := range a {
		if v < m {
			m = v
		}
	}
	return m
}

func sum(a ints) int {
	if len(a) == 0 {
		return 0
	}
	sum := 0
	for _, e := range a {
		sum += e
	}
	return sum
}
func find(n int, a ints) int {
	for i, v := range a {
		if n == v {
			return i
		}
	}
	return -1
}

C++: //This template was last modified on 2/1/2020.
//Define many functions and words.
//The functions I have defined start with a capital letter.
#include <bits/stdc++.h>
using namespace std;
//C++ words.

#define MOD 1000000007
//#define MOD 998244353

typedef long long ll;
typedef vector<ll> vl;
typedef vector<double> vd;
typedef vector<vl> matrix;//A(n, vl(m));
typedef vector<string> vs;
typedef pair<ll,ll> pl;
typedef vector<pl> vp;
typedef pair<double,double> pd;
typedef vector<pd> vpd;
typedef vector<bool> vb;
typedef map<ll,ll> mapl;
typedef priority_queue<ll> pque;
#define nl "\n"s
#define rep(i,n) for(ll i=0LL; i<(n); i++)
#define INF 1001001001001001001
#define PI 3.14159265358979323846
#define SP << " "s <<
#define PB push_back
#define MP make_pair
#define F first
#define S second
#define All(V) V.begin(),V.end()
#define Sortup(V) sort(All(V))
#define Sortdown(V) sort(V.rbegin(), V.rend())
#define Atleast(key, V) lower_bound(All(V), key)
#define Largerthan(key, V) upper_bound(All(V), key)

ll IN(){ll x; cin>>x; return x;}
void VIN(vl &x){rep(i, x.size()) cin>>x[i];}
#define endYes do{cout << "Yes" << nl; return 0;}while(0)
#define endYES do{cout << "YES" << nl; return 0;}while(0)
#define endNo  do{cout << "No" << nl; return 0;}while(0)
#define endNO  do{cout << "NO" << nl; return 0;}while(0)
#define endS(str) do{cout << str << nl; return 0;}while(0)


//Mathmatical functions.

template<class T>bool Chmax(T &a, T b){if(a<b){a=b;return 1;}return 0;}
template<class T>bool Chmin(T &a, T b){if(a>b){a=b;return 1;}return 0;}
template<class T>double Dist(T x,T y,T X,T Y){return sqrt( (x-X)*(x-X)+(y-Y)*(y-Y) );}
ll Digit(ll N){ll res=0;while(N) res++, N/=10;return res;}
bool Bit(ll subset, ll Rsift){ return ((subset)>>(Rsift))&1; }
ll Gcd(ll a,ll b){ return b?Gcd(b,a%b):abs(a); }
ll Lcm(ll A,ll B){ return A/Gcd(A,B)*B; }
ll Lpow(ll e,ll x){ll res=1LL;while(x){if(x&1)res*=e;e*=e;x/=2;}return res;}
ll Pow(ll e,ll x){ll res=1LL;while(x){if(x&1)res=(1LL*res*e)%MOD;e=(1LL*e*e)%MOD;x/=2;}return res;}
void Mul(ll &a,ll b){ a=1LL*a*b%MOD; }
void CumuSum(vl &A){rep(i,A.size())if(i)A[i]+=A[i-1];}
void Eratos_prime(vb &is_prime){//1-indexed
    ll N=is_prime.size()-1;
    rep(i, N) is_prime.at(i) = true;
    is_prime.at(0) = is_prime.at(1) = false;
    for(ll i=2; i*i<=N; i++) if(is_prime.at(i)) {
        for(ll j=i+i; j<=N; j+=i) is_prime.at(j) = false;
    }
}
void Primefact(ll N, mapl &elem){
    for(ll i=2; i*i<=N; i++) {
        while(N%i==0) {
            elem[i]++;
            N /= i;
        }
    }
    if(N>1) elem[N]++;
}


/*
//Topological sort  O(|V|+|E|)
vl g[100100];
vb used(100100);
vl Sortedgraph;

void dfs_Tsort(ll u) {
  if(used[u]) return;
  used[u] = true;
  for(auto x: g[u]) dfs_Tsort(x);
  Sortedgraph.push_back(u);
}

//N:=|V|
void Topo_sort(ll N) {
  rep(i, N) dfs_Tsort(i);
  reverse(All(Sortedgraph));
}
*/

/*
//Warshall floyd  O(N**3)
#define MAX_V 100
matrix d(MAX_V, vl(MAX_V));

void warshall_floyd(ll V){
    rep(k, V) rep(i, V) rep(j, V){
        Chmin(d[i][j], d[i][k] + d[k][j]);
    }
}
*/

/*
//Combination in MOD  O(N)
//Constraints 1<=k<=n<10^7  and  MOD is prime  and MOD>n
const ll MAX=1001001;
vl fac(MAX), finv(MAX), inv(MAX);
void COMinit() {
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for (ll i = 2; i < MAX; i++){
        fac[i] = fac[i - 1] * i % MOD;
        inv[i] = MOD - inv[MOD%i] * (MOD / i) % MOD;
        finv[i] = finv[i - 1] * inv[i] % MOD;
    }
}
//Combination
ll COM(ll n, ll k){
    if (n<k or n<0 or k<0) return 0;
    return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}
*/

//////////////////////////////////////////////////////////////////////////
//////////////////////////////////////////////////////////////////////////
//////////////////////////////////////////////////////////////////////////
// solution comes here

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

    ll N; cin >> N;
    vl fi(N+1);
    fi[0] = fi[1] = 1;
    for(ll i=2; i<=N; i++) fi[i] = fi[i-1]+fi[i-2];
    cout << fi[N] << nl;
}

C++: #include<iostream>
using namespace std;
int main(){
	int dp[45];
	dp[0]=1;
	dp[1]=1;
	for(int i=2; i<45; i++){
		dp[i]=dp[i-1]+dp[i-2];
	}
	int n;
	cin>>n;
	cout<<dp[n]<<endl;
	return 0;
}