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 < (int)(n); i++)

using namespace std;

namespace utils{
  template <typename T> void print(vector<vector<T>> mat) {
    rep (i, mat.size()) {
      rep (j, mat[0].size()) cout << mat[i][j] << ' ';
      cout << endl;
    }
  }

  template <typename T> void print(vector<T> v) {
    rep (i, v.size()) cout << v[i] << ' ';
    cout << endl;
  }

  template <typename T> pair<T, T> shape(vector<vector<T>> mat) {
    int d1, d2;

    d1 = mat.size();
    if (d1 > 0) d2 = mat[0].size();
    else int d2 = 0;
    cout << "(" << d1 << ", " << d2 << ")" << endl;
    return make_pair(0, 0);
  }

  template <typename T> vector<vector<T>> empty(int n, int m) {
    vector<vector<T>> mat(n, vector<T>(m));
    return mat;
  }
}


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

  vector<int> dp(N+1);
  fill(dp.begin(), dp.end(), 0);
  dp[0] = 1;
  dp[1] = 1;

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

  cout << dp[N] << endl;
}

C++: /*
** 斐波那契数列 使用动态规划来避免重复的计算
*/

# include <cstdio>
# include <cstring>

const int MAX = 44 + 5;

int n, dp[MAX];

// 记忆化递归 
/*
int fib(int i) {
    if (dp[i] != 0) {
        return dp[i];
    }
    if (i <= 1) {
        return 1;
    }
    dp[i] = fib(i - 1) + fib(i - 2);
    return dp[i];
}
*/

// 动态规划

int fib(int t) {
    dp[0] = dp[1] = 1;
    for (int i = 2; i <= t; i++) {
        dp[i] = dp[i - 1] + dp[i - 2];
    }
    return dp[t];
}

void solve() {
    scanf("%d", &n);
    memset(dp, 0, sizeof(dp));
    printf("%d\n", fib(n));
}

int main() {
    // freopen("infile", "r", stdin);
    // freopen("outfile", "w", stdout);
    solve();
    return 0;
}

C++: #include <bits/stdc++.h>
#define int long long
#define main signed main()
#define loop(i, a, n) for (int i = (a); i < (n); i++)
#define rep(i, n) loop(i, 0, n)
#define forever while (true)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define prec(n) fixed << setprecision(n)
template<typename A> using V = std::vector<A>;
template<typename A> using F = std::function<A>;
template<typename A, typename B> using P = std::pair<A, B>;
using pii = P<int, int>;
using vi = V<int>;
using vd = V<double>;
using vs = V<std::string>;
using vpii = V<pii>;
using vvi = V<vi>;
using vvpii = V<vpii>;
constexpr int INF = sizeof(int) == sizeof(long long) ? 1000000000000000000LL : 1000000000;
constexpr int MOD = 1000000007;
constexpr double PI = acos(-1);
template<typename A, typename B> bool cmin(A &a, const B &b) { return a > b ? (a = b, true) : false; }
template<typename A, typename B> bool cmax(A &a, const B &b) { return a < b ? (a = b, true) : false; }
using namespace std;

template<typename Integral = int> Integral fibonacci(const int &n) {
  static std::vector<Integral> dp(2, 1);
  int prev = dp.size();
  if (prev < n + 1) {
    dp.resize(n + 1);
    loop(i, prev, dp.size()) dp[i] = dp[i - 1] + dp[i - 2];
  }
  return dp[n];
}

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

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

int main(void){
	int a=0, b=1, n;
	cin>>n;
	if (n<0) return NULL;

	for (int i=-1; i<n; i++){
		a += b;
		swap(a,b);
	}
	cout<<a<<endl;
	return 0;
}

C++: #include "bits/stdc++.h"

using namespace std;

long long fib(long long n, vector<long long>& memo) {
    if (memo[n] >= 0) {
        return memo[n];
    }

    if (n == 0) {
        return 1;
    }
    else if (n == 1) {
        return 1;
    }
    else {
        long long ret = fib(n - 1, memo) + fib(n - 2, memo);
        memo[n] = ret;
        return ret;
    }
}

void Main() {
    long long n;
    cin >> n;

    vector<long long> memo(n + 10, -1LL);
    memo[0] = 1;
    memo[1] = 1;
    long long ans = fib(n, memo);
    cout << ans << endl;
}

int main() {
    std::cout << std::fixed << std::setprecision(15);
    Main();
    return 0;
}

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

typedef long long ll;

ll table[45];
bool flg[45];

ll fib(int n){
    if(flg[n])return table[n];
    else{
        flg[n]=true;
        return table[n]=fib(n-1)+fib(n-2);
    }
}


int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    table[0]=table[1]=1;
    flg[0]=flg[1]=true;
    int n;
    cin >> n;
    cout << fib(n) << endl;
}

C++: #include <bits/stdc++.h>
using namespace std;
//using ll = long long;
#define MAX 100

int main(void) {
  int n;
  cin >> n;
  
  vector<int> F(50);
  F.at(0) = F.at(1) = 1;
  for (int i = 2; i <= n; i++) F.at(i) = F.at(i-1) + F.at(i-2);

  cout << F.at(n) << endl;


}