Go: package main

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

var scanner = bufio.NewScanner(os.Stdin)

func nextString() string {
	scanner.Scan()
	return scanner.Text()
}

func nextInt() int {
	n, err := strconv.Atoi(nextString())
	if err != nil {
		fmt.Printf("strconv.Atoi failed: %v\n", err)
	}
	return n
}

func main() {
	scanner.Split(bufio.ScanWords)

	n := nextInt()
	f := 1
	for i := 1; i <= n; i++ {
		f *= i
	}
	fmt.Println(f)
}

C++: #include<iostream>

using namespace std;

long long factorial(long long n){
  long long int ans;
  if(n==0)
    ans=1;
  else
    ans =n*factorial(n-1);
  return ans;
}

int main(){
  long long  n=0;
  cin>>n;

  long long int ans=1;
  ans=factorial(n);

  cout<<ans<<endl;
}

C++: #include<iostream>

int main()
{
	int n;

	unsigned long long int s=1;

	std::cin >> n;

	for(int i=1;i<=n;++i)
	{
		s*=i;
	}

	std::cout << s << '\n';
}

C++: #include<iostream>

using namespace std;

int main()
{
     int counter, n, fact = 1;

     cin>>n;

     for (int counter = 1; counter <= n; counter++)
     {
         fact = fact * counter;
     }

     cout<<fact;
 }

C++: #include <iostream>

using namespace std;

int main() {
  int n;
  long long int result = 1;
  cin >> n;
  for (int i = n; i > 0; i--) {
    result *= i;
  }
  cout << result << endl;
  return 0;
}

C++: #include <cstdio>

int kaijo(int n);
unsigned int ans;

int main(void)
{
    int n;
    scanf("%d", &n);
    
    kaijo(n);
    printf("%u\n", ans);
    
}

int kaijo(int n)
{
    if (n == 1) return 1;
    
    ans = n * kaijo(n - 1);
    
    return (ans);
}

C++: #include <iostream>
using namespace std;
int main(void){
    long int n, ans=1;
    cin >> n;
    for(int i=n; i>0; i--){
        ans *= i;
    }
    cout << ans << endl;
    return 0;
}

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

long long int factorial(int n);

int main(){
	
    int i;
	
	cin >> i;
	
	cout << factorial(i) << endl;
	
	return 0;
}

long long int factorial(int n){

	if(n==1){
		return 1;
	}else{
		return n*factorial(n-1);
	}
}

C++: //by azidoazideazide(c2n14)
#include<iostream>
#include<string>
#include<cmath>
#include<algorithm> //#include<map>
#include<vector>
using namespace std;
typedef long long ll;
//#include<fstream>
//ifstream fin("rps.in");
//ofstream fout("rps.out");
//#define pb push_back
ll fact(ll n){
  if(n==1) return 1;
  else return n*fact(n-1);
}
int main(){
	ios::sync_with_stdio(0);
	ll n;
  cin>>n;
  cout<<fact(n)<<endl;
return 0;
}

C++: #define _USE_MATH_DEFINES
#include <iostream>
#include <queue>
#include <vector>
#include <math.h>
#include <algorithm>
#include <iomanip>
#include <string>
#include <stack>
using namespace std;

int main(){
	int n;
	long long int result = 1;
	cin >> n;
	for (; n > 0; --n) {
		result *= n;
	}
	cout << result << endl;
	return 0;
}

C++: #include<iostream>
double input=0;

void factorial(double& i__)
{
	double result=1;
	for(int i=i__;i>0;i--)
	{
		result*=i;
	}

	std::cout<<result<<std::endl;

}

int main()
{
	std::cin>>input;
	do
	{	
		factorial(input);
		std::cin>>input;
	}while(input<=20&&input>=0);


	return 0;
}

C++: #include<iostream>
using namespace std;
int fac(unsigned long long in)
{
    if(in<=1)
        return in;
    else
        return in*(fac(in-1));
}
int main()
{
    unsigned long long in,f;
    cin>>in;
    f=fac(in);
    cout<<f;
    return 0;
}

C++: #include<iostream>
#include<iomanip>
#include<algorithm>
#include<cctype>
#include<cmath>
#include<cstdio>
#include<set>
#include<stack>
#include<string>
#include<sstream>
#include<map>
#include<queue>
#include<vector>
using namespace std;

int main() {
	int n;
	long long s = 1;
	cin >> n;
	while (n)s *= n--;
	cout << s << endl;
	return 0;
}

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

#define pb(n) push_back(n)
#define fi first
#define se second
#define np string::npos
#define X real()
#define Y imag()
#define value(x,y,w,h) (x >= 0 && x < w && y >= 0 && y < h)
#define all(r) (r).begin(),(r).end()
#define gsort(st,en) sort((st),(en),greater<int>())
#define vmax(ary) *max_element(all(ary))
#define vmin(ary) *min_element(all(ary))
#define debug(x) cout<<#x<<": "<<x<<endl
#define fcout(n) cout<<fixed<<setprecision((n))
#define scout(n) cout<<setw(n)

#define rep(i,n) for(int i = 0; i < (int)(n);++i)
#define repc(i,a,b) for(int i = (a);i < (int)(b);++i)
#define repi(it,array) for(auto it = array.begin(),end = array.end(); it != end;++it)
#define repa(n,array) for(auto &n :(array))

typedef long long ll ;
typedef deque<int> di ;
typedef deque<ll> dl ;
typedef map<string,int> dict;
typedef complex<double> comd;
typedef pair<int,int> pii;

constexpr int imax = ((1<<30)-1)*2+1 ;
constexpr int inf = 100000000;
constexpr double PI = acos(-1.0) ;
double eps = 1e-10 ;
const int dy[] = {-1,0,1,0};
const int dx[] = {0,-1,0,1};

double CalcDist(comd p1, comd p2){
  return sqrt(pow(p1.X - p2.X,2.0) + pow(p1.Y -p2.Y,2.0));
}

template <typename T>
void out(deque < T > d)
{
  for(size_t i = 0; i < d.size(); i++)
  {
    debug(d[i]);
  }
}

template<typename T>
T ston(string& str, T n){
  istringstream sin(str) ;
  T num ;
  sin >> num ;
  return num ;
}

int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  int n;
  cin >> n;
  int f[20] ;
  ll ans = 1;
  rep(i,n) ans*=i+1;
  cout << ans << endl;
  return 0;
}

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

int main(){
int n;
bool a=false;
int ans[30];
ans[0]=1;
for(int i=1;i<30;i++){
ans[i]=0;}
cin>>n;
for(int i=2;i<n+1;i++){
for(int j=29;j>-1;j--){
ans[j]*=i;
if(ans[j]>=10){
ans[j+1]+=(ans[j]-ans[j]%10)/10;
ans[j]%=10;
}
}
}
for(int i=29;i>-1;i--){
if(ans[i]!=0){
a=true;}
if(a){
cout<<ans[i];}}
cout<<endl;}

C++: #include <cstdio>
#include <algorithm>
#include <functional>
#include <stack>
#include <cmath>
using namespace std;

#define REP(i, n) for(int i = 0;i < n;i++)
#define REPR(i, n) for(int i = n;i >= 0;i--)
#define FOR(i, m, n) for(int i = m;i < n;i++)
#define llong long long

int factorial(int n) {
  if(n == 0) return 1;
  return n * factorial(n-1);
}

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

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

long int factorial(long int n, long int res){
    if (n == 1) return res;
    return factorial(n-1, res * n);
}

int main(){
    long int n;
    cin >> n;
    cout << factorial(n, 1) << endl;;
    return 0;
}

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

long long factorial(long long n){   // 再帰関数
  if(n==1){
    return n;
  }else{
    n*=factorial(n-1);
  }
}

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

  if(n<0){
    cout << "計算できません。" << endl;
  }else if(n==0 || n==1){
    cout << 1 << endl;
  }else{
    cout << factorial(n) << endl; 
  }
  return 0;
}

C++: #include <iostream>
#define MAX 5
using namespace std;

void HELLO();
int max(int x1, int x2);
int min(int x1, int x2);
int sum(int* array);
int fact(int n);

int main(){
	
	int n;
	cin >> n;
	
	cout << fact(n) << endl;
	
	return 0;
}

void HELLO(){ cout << "Hello!!" << endl; }

int max(int x1, int x2){ return x1 > x2 ? x1 : x2; } 
int min(int x1, int x2){ return x1 < x2 ? x1 : x2; }

int sum(int* array){
	int sumup = 0;
	for(int i = 0; i < MAX; i++) sumup += array[i];
	return sumup;
}

int fact(int n){
	if(n < 1) return 1;
	return n * fact(n - 1);
}

C++: #include<iostream>
#include<iomanip>
#include<algorithm>
#include<cctype>
#include<cmath>
#include<cstdio>
#include<set>
#include<stack>
#include<string>
#include<sstream>
#include<map>
#include<queue>
#include<vector>

using namespace std;

int main() {
	int n,ans;
	cin >> n;
	1 <= n <= 20;
	ans = n;
	for(int i=n-1;i>1;i--){
		ans *= i;
	}
	cout << ans << endl;
	return 0;
}

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

int main()
{
	int n;
	long long int ans = 1;
	int num;

	cin >> n;

	for(int i = n+1; i>1; i--)
	{
		ans *= (i-1);
	}

	cout << ans << endl;

	return 0;
}