Go: package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

func getScanner(fp *os.File) *bufio.Scanner {
	scanner := bufio.NewScanner(fp)
	scanner.Split(bufio.ScanWords)
	scanner.Buffer(make([]byte, 500001), 500000)
	return scanner
}

func getNextString(scanner *bufio.Scanner) string {
	scanner.Scan()
	return scanner.Text()
}

func getNextInt(scanner *bufio.Scanner) int {
	i, _ := strconv.Atoi(getNextString(scanner))
	return i
}

func main() {
	fp := os.Stdin
	if len(os.Args) > 1 {
		fp, _ = os.Open(os.Args[1])
	}

	scanner := getScanner(fp)
	writer := bufio.NewWriter(os.Stdout)

	n := getNextInt(scanner)

	fmt.Fprintln(writer, fib(n))
	writer.Flush()

}

func fib(n int) int {
	if n <= 1 {
		return 1
	}
	dp := make([]int, n+1)
	dp[0] = 1
	dp[1] = 1
	for i := 2; i <= n; i++ {
		dp[i] = dp[i-2] + dp[i-1]
	}
	return dp[n]
}

C++: /**
 * @Author: yujirotakahashi
 * @Date:   2020-05-17T20:21:41+09:00
 * @Last modified by:   yujirotakahashi
 * @Last modified time: 2020-05-25T00:28:40+09:00
 */

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

/*******  All Required define Pre-Processors and typedef Constants *******/
#define all(cont) cont.begin(), cont.end()
#define rall(cont) cont.end(), cont.begin()
#define rep(i,n) for(int i=0; i<(n); ++i)
#define rep1(i,n) for(int i=1; i<=(n); ++i)
#define Dcout(a) cout << setprecision(20) << a << endl
#define MP make_pair
#define PB push_back
#define EPS 1e-9
#define PI 3.1415926535897932384626433832795
#define MOD 1000000007
//const ll INF = (1LL << 60);
//const double pi=acos(-1.0);
using ll = long long;
using PAIR = pair<int, int>;
#define debug cout << "line : " << __LINE__ << " debug" << endl
/****** Template of some basic operations *****/
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; }
/**************************************/

/******** User-defined Function *******/
using Graph = vector<vector<int>>;
int dx[4] = {-1,0,0,1};
int dy[4] = {0,1,-1,0};
/**************************************/

/********** Main()  function **********/
int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);

  int n; cin >> n;
  ll dp[50];
  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;
}
/********  Main() Ends Here *************/

C++: #include <bits/stdc++.h>

using namespace std;
using ll =long long;
#define SORT(a) sort((a).begin(),(a).end())
#define rSORT(a) reverse((a).begin(),(a).end())
#define For(i, a, b)    for(int i = (a) ; i < (b) ; ++i)
#define rep(i, n)       For(i, 0, n)
#define debug(x)  cerr << #x << " = " << (x) << endl;
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; }
//Write From this Line

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

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

int main()
{
  int n;
  cin >> n;
  if (n <= 1)
  {
    cout << 1 << endl;
    return 0;
  }
  vector<int> dp(n + 1, 1);
  for (int i = 2; i <= n; i++)
  {
    dp.at(i) = dp.at(i - 1) + dp.at(i - 2);
  }
  cout << dp.at(n) << endl;
}

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

C++: # include <bits/stdc++.h>
# define ll int64_t
# define rep(i,n) for(ll i=0;i<n;i++)
# define rrep(i,n) for(ll i=1;i<=n;i++)
# define ALL(x) (x).begin(), (x).end()
# define SZ(x) ((int)(x).size())
# define pb push_back
# define mod 1000000007
# define vec vector
#define dump(x) cerr<<#x<<"="<<x<<endl
using namespace std;

bool compare_by_b(pair<string,ll> a,pair<string,ll> b){
    if(a.second != b.second) return a.second<b.second;
    else return a.first<b.first;
}

bool my_compare(pair<string,ll> a,pair<string,ll> b){
    
    if(a.first != b.first) return a.first<b.first;
    if(a.second != b.second) return a.second>b.second;
    else return true;
}

ll factorial(ll n){
    ll x=1;
    rrep(i,n) (x*=i)%=mod;
    return x;
}

ll gcd(ll a,ll b)
{
   if (a%b == 0) return(b);
   else return(gcd(b,a%b));
}

ll lcm(ll a,ll b)
{
   return a/gcd(a,b)*b;
}

//累乗だってさ
ll modpow(ll a,ll n,ll mod1) {
    ll res=1;
    while(n>0){
        if(n&1) res=res*a%mod1;
        a = a*a%mod1;
        n >>= 1;
    }
    return res;
}
//逆元だってさ
ll modinv(ll a,ll mod1) {
    return modpow(a, mod1 - 2, mod1);
}

const ll MAX = 1000000;
const ll MOD = 1000000007;

ll fac[MAX], finv[MAX], inv[MAX];

// テーブルを作る前処理
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;
    }
}

// 二項係数計算
ll COM(ll n, ll k){
    if (n < k) return 0;
    if (n < 0 || k < 0) return 0;
    return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}


void solve(){
    
}

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    
    ll n;
    cin>>n;
    ll dp[55];
    dp[0]=1;
    dp[1]=1;
    for(ll i=2;i<n+1;i++){
        dp[i]=dp[i-1]+dp[i-2];
    }
    cout<<dp[n]<<endl;
    return 0;
}