Go: package main

import "fmt"

func main() {
	var n int
	fmt.Scan(&n)

	x, y := int64(0), int64(1)
	for i := 0; i < n; i++ {
		x, y = y, x+y
	}

	fmt.Println(x)
}

C++: /**
 * @copyright (c) 2020 Daisuke Hashimoto
 */

#include <cstdint>
#include <iostream>
#include <string>

constexpr int32_t kMaxNumberOfIndex = 100;

void CallFibonacciNumber(std::istream &input_stream);

class FibonacciNumber {
 public:
  FibonacciNumber() noexcept;
  ~FibonacciNumber() noexcept;
  int32_t Calculate(const int32_t n);

 private:
  FibonacciNumber(const FibonacciNumber &obj) = delete;
  FibonacciNumber &operator=(const FibonacciNumber &obj) = delete;
  FibonacciNumber(FibonacciNumber &&obj) = delete;
  FibonacciNumber &operator=(FibonacciNumber &&obj) = delete;

 private:
  int32_t values_[kMaxNumberOfIndex];
};

void CallFibonacciNumber(std::istream &input_stream) {
  input_stream.tie(0);
  std::ios::sync_with_stdio(false);
  FibonacciNumber *fibonacci_number = new FibonacciNumber();
  try {
    int32_t n;
    input_stream >> n;
    std::cout << fibonacci_number->Calculate(n) << std::endl;
  } catch (...) {
    std::cerr << "ERROR: CallFibonacciNumber()" << std::endl;
    throw;
  }
  delete fibonacci_number;
}

// ****************************************************

FibonacciNumber::FibonacciNumber() noexcept {
  values_[0] = 1;
  values_[1] = 1;
}
FibonacciNumber::~FibonacciNumber() noexcept {}

int32_t FibonacciNumber::Calculate(const int32_t n) {
  for (int32_t index = 2; index <= n; ++index) {
    values_[index] = values_[index - 1] + values_[index - 2];
  }
  return values_[n];
}

int main(int argc, char *argv[]) {
  try {
    CallFibonacciNumber(std::cin);
  } catch (...) {
    std::cerr << "ERROR: main()" << std::endl;
  }
  return 0;
}

C++: #include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;
typedef long long ll;
const int MAX=50;
ll f[MAX];
ll fib(int n){
	f[0]=f[1]=1;
	for(int i=2;i<=n;i++){
		f[i]=f[i-1]+f[i-2];
	}
	return f[n];
} 

int main(){
	int n;
	scanf("%d",&n);
	printf("%lld\n",fib(n));
	return 0;
}

C++: #include <iostream>

using namespace std;

int fib(int n);

int main() {
    int n;

    //??\???
    cin >> n;

    //??????
    cout << fib(n) << endl;

    return 0;
}

int fib(int n){
    /* ??????1 */
  if(n <= 1) return 1;
  return fib(n-1) + fib(n-2);
}

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

int f[1000000] = {};

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

int fib2(int n){
    int ff[100000] = {};
    ff[0] = 1;
    ff[1] = 1;
    for(int i = 2; i <= n; i++){
        ff[i] = ff[i-2] + ff[i-1];
    }
    return ff[n];
}

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

    cout << fib2(n) << endl;
    return 0;
}