Go: package main

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

// I/O
type Scanner struct {
	sc *bufio.Scanner
}

func NewScanner() *Scanner {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	sc.Buffer(make([]byte, 1024), int(1e+9))
	return &Scanner{sc}
}

func (s *Scanner) nextStr() string {
	s.sc.Scan()
	return s.sc.Text()
}

func (s *Scanner) nextInt() int {
	i, e := strconv.Atoi(s.nextStr())
	if e != nil {
		panic(e)
	}
	return i
}

func (s *Scanner) nextFloat() float64 {
	f, e := strconv.ParseFloat(s.nextStr(), 64)
	if e != nil {
		panic(e)
	}
	return f
}

func (s *Scanner) nextRuneSlice() []rune {
	return []rune(s.nextStr())
}

func (s *Scanner) nextIntSlice(n int) []int {
	res := make([]int, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextInt()
	}
	return res
}

func (s *Scanner) nextFloatSlice(n int) []float64 {
	res := make([]float64, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextFloat()
	}
	return res
}

// Arithmetic
func max(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m < i {
			m = i
		}
	}
	return m
}

func min(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m > i {
			m = i
		}
	}
	return m
}

func abs(x int) int {
	if x > 0 {
		return x
	}
	return -x
}

func pow(x, y int) int {
	res := 1
	for i := 0; i < y; i++ {
		res *= x
	}
	return res
}

func ceil(a, b int) int {
	if a%b == 0 {
		return a / b
	} else {
		return a/b + 1
	}
}

// Sort
type RuneSlice []rune

func (a RuneSlice) Len() int           { return len(a) }
func (a RuneSlice) Less(i, j int) bool { return a[i] < a[j] }
func (a RuneSlice) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }

// Main
func main() {
	sc := NewScanner()
	wtr := bufio.NewWriter(os.Stdout)
	N := sc.nextInt()
	dp := make([]int, N+1)
	dp[0] = 1
	dp[1] = 1
	for i := 2; i <= N; i++ {
		dp[i] = dp[i-1] + dp[i-2]
	}

	fmt.Fprintln(wtr, dp[N])
	wtr.Flush()
}

C++: #include <stdio.h>

int main() {
    int a = 1, b = 1, c = 2, i = 2;
    int n;
    scanf("%d", &n);
    while (i < n) {
        a = b;
        b = c;
        c = a + b;
        i++;
    }
    if (n<2){
        printf("1\n");
    }else{
        printf("%d\n", c);
    }
    return 0;
}

C++: //
//  main.cpp
//  ALDS1_10_A:FibonacciNumber
//
//  Created by Kang on 2020/8/12.
//  Copyright © 2020 Kang. All rights reserved.
//

#include <cstdio>
#include <cstring>
using namespace std;


int fiboFromTop(int n, int fibo[]) {
    if (fibo[n] != 0) {
        return fibo[n];
    }
    
    if (n == 0 || n == 1) {
        fibo[n] = 1;
        return 1;
    }
    else {
        fibo[n - 1] = fiboFromTop(n-1, fibo);
        fibo[n - 2] = fiboFromTop(n - 2, fibo);
        return fibo[n - 1] + fibo[n - 2];
    }
    
    
    return 0;
}

int fiboFromBottom(int n) {
    if (n == 0 || n == 1) {
        return 1;
    }
    int fibo[45];
    fibo[0] = 1;
    fibo[1] = 1;
    for (int i = 2; i <= n; i++) {
        fibo[i] = fibo[i-1] + fibo[i - 2];
    }
    return fibo[n];
}

int main(int argc, const char * argv[]) {
    // insert code here...
    int n;
    int fibonacci[45];
    memset(fibonacci, 0, 45 * sizeof(int));
    scanf("%d", &n);
    
    // printf("%d\n", fiboFromTop(n, fibonacci));
    printf("%d\n", fiboFromBottom(n));
    
    return 0;
}

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

int main(){
  int n,for_n=1,pre_n=1;

  cin >> n;
  for(int i=0;i<=n;i++){
    if((i==0) || (i==1)){
      continue;
    }else{
      int swp=for_n;

      for_n += pre_n;
      pre_n = swp;
    }
  }
  cout << for_n << endl;
}

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

int main()
{
    int fib[50] = {1, 1};
    int n;
    cin >> n;    
    
    for(int i = 2; i <= n; ++i){
        fib[i] = fib[i-1] + fib[i-2];
    }
    cout << fib[n] << endl;
}

C++: #include<iostream>

using namespace std;

int fib(int n);

int main() {
  int n;

  //入力
  cin >> n;

  //出力
  cout << fib(n) << endl;

  return 0;
}

int fib(int n){
  int memo[1000];

  if(n==0 || n == 1){
    return memo[n] = 1;
  }else if(memo[n] != 0){
    return memo[n];
  }else{
    return memo[n] = fib(n-1) + fib(n-2);
  }
}

C++: #include <iostream>
#include <algorithm>
#include <cstdio>
#include <limits>

const int N = 102;

long m[N][N], p[N+1];

int matrixChainOrder(int n){

  for(int i=1; i<n; i++){ m[i][i] = 0; }

  for(int l=2; l<n; l++){
    for(int i=1; i < n - l + 1; i++){
      int j = i+l-1;
      m[i][j] = std::numeric_limits<long>::max();
      for(int k=i; k<=j-1; k++){
        m[i][j] = std::min(m[i][j], m[i][k] + m[k+1][j] + p[i-1]*p[k]*p[j]);
      }
    }
  }
  return m[1][n - 1];
}

int main(){
  int n ;
  std::cin >> n; //number of matrix

  for(int i=1; i<=n; i++){
    std::cin >> p[i-1] >> p[i];
  }
  // for (int i = 0; i <=n; ++i) std::cout << p[i] << std::endl;
  std::cout << matrixChainOrder(n + 1) << std::endl;

  return 0;
}