Go: package main

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

var sc = bufio.NewScanner(os.Stdin)

func read() string {
	sc.Scan()
	return sc.Text()
}

func main() {
	sc.Split(bufio.ScanLines)
	n, _ := strconv.Atoi(read())
	sum := 1
	for i := n; i > 0; i-- {
		sum *= i

	}
	fmt.Println(sum)
}

C++: /////////////////////////////////////////////////////////
//
//  c/temp.cpp file
//  Last Updated: 2018-10-23 ...Maybe
//
//    I hope you adding this code to the setting file
//    alias g++='g++ -std=c++1y -DDEBUG_LOCAL'
//
/////////////////////////////////////////////////////////

#include <bits/stdc++.h>

using namespace std;

#define fi first
#define se second
#define mp make_pair
#define pb push_back

//#define int long long

#define _overload3(_1,_2,_3,name,...) name
#define _REP(i,n) REAP(i,0,n)
#define REAP(i,a,b) for(int i=int(a);i<int(b);++i)
#define REP(...) _overload3(__VA_ARGS__,REAP,_REP,)(__VA_ARGS__)

#define _REPR(i,n) REAPR(i,n,0)
#define REAPR(i,a,b) for(int i=int(a-1);i>=int(b);--i)
#define REPR(...) _overload3(__VA_ARGS__,REAPR,_REPR,)(__VA_ARGS__)

#define ALL(a) a.begin(),a.end()
#define rALL(a) a.rbegin(),a.rend()

#define coutALL(a) {int loop_coutALL=0;for(auto e:a) cout<<(loop_coutALL++?" ":"")<<e; cout<<endl;}

#define coutYN(a) cout<<((a)?"YES":"NO")<<endl;
#define coutYn(a) cout<<((a)?"Yes":"No")<<endl;
#define coutyn(a) cout<<((a)?"yes":"no")<<endl;

#define pcnt __builtin_popcount
#define buli(x) __builtin_popcountll(x)

const int INF=1145141919;
//const long long INF=114514191911451419;
const int MOD=(int)1e9+7;
const double EPS=1e-12;
const int dx[]={1,0,-1,0},dy[]={0,1,0,-1};
//const int dx[]={-1,-1,-1,0,1,1,1,0},dy[]={-1,0,1,1,1,0,-1,-1};

using vi=vector<int>;
using vvi=vector<vi>;
using vs=vector<string>;

typedef pair<int,int> pii;
typedef pair<int,string> pis;
typedef pair<string,int> psi;
typedef pair<string,string> pss;

typedef long long ll;

template<typename T> istream &operator >> (istream &is, vector<T> &v){for(T &x:v) is>>x;return is;}
template<typename T> ostream &operator << (ostream &os, vector<T> &v){int i=0;for(T &x:v) os<<(i++?" ":"")<<x;return os;}

ll rev(ll n){ll x=0;for(;n>0;){x=x*10+n%10;n/=10;}return x;}

ll upper(ll n,ll m){return (n+m-1)/m;};
ll rounding(ll n){return (long double)n+0.5;};

bool inG(ll x,ll n){return 0<=x && 0<n;}
bool outG(ll x,ll n){return x<0 || n<=x;}

inline int qp(int a,ll b){if(!b)return 1;int ans=1;do{if(b&1)ans=1ll*ans*a;a=1ll*a*a;}while(b>>=1);return ans;}
inline int qp(int a,ll b,int mo){if(!b)return 1;int ans=1;do{if(b&1)ans=1ll*ans*a%mo;a=1ll*a*a%mo;}while(b>>=1);return ans;}

inline ll fac(ll k,ll n){ll a=1;for(int i=0;i<n;i++)a*=k--;return a;}
inline ll fac(ll k,ll n,int mo){ll a=1;for(int i=0;i<n;i++)a*=k--,a%=mo;return a;}

inline int dsum(ll n){int a=0;for(;n;n/=10)a+=n%10;return a;}

struct Arithmetic{Arithmetic(){cin.tie(0);ios::sync_with_stdio(0);cout<<fixed<<setprecision(20);}};

//#define DEBUG_LOCAL

#ifdef DEBUG_LOCAL
template<typename T> void deb(T a){cerr<<"deb: "<<a<<"です"<<endl;}
#define debl {cerr<<"debug: "<<__LINE__<<"行目だ"<<endl;}
void what_cr(){cout<<__GCC_ATOMIC_CHAR16_T_LOCK_FREE<<" ←？"<<endl;}
//ori_func S

//ori_func E
#else
template<typename T>void deb(T a){}
#define debl
void what_cr(){}void t_t(){}
#endif

signed main(){

  Arithmetic Exception;

  int n;
  cin>>n;

  ll ans=1;
  REP(i,1,n+1) ans*=i;

  cout<<ans<<endl;

  return 0;

}

C++: #include <iostream>
#include <algorithm>
#include <vector>
#include <cstdio>
#include <string>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <cmath>
#include <functional>
#include <numeric>
#define fi first
#define se second
using namespace std;
bool value(int y,int x,int R,int C){return 0<=y&&y<R&&0<=x&&x<C;}
typedef pair<int,int> pii;
typedef long long ll;
typedef vector<int> vi;
typedef vector<long long > vll;
typedef vector< vi > vvi;
double pie=acos(-1);
int INF=10000009;
int dx[4] = { 0,-1,0,1 };
int dy[4] = { -1,0,1,0 };
int main() {
	int n;
	ll ans=1;
	cin>>n;
	for(int i=1;i<=n;i++){
		ans*=i;
	}
	cout<<ans<<endl;
}

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

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

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

typedef uint64_t u64;

int main() {

  u64 n;
  std::cin >> n;

  u64 res = 1;
  for(u64 i = 1; i <= n; ++i) {
    res *= i;
  }

  std::cout << res << std::endl;
  
  return 0;
}

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

using namespace std;

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

C++: #include <stdio.h>

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

	scanf("%d", &n);
	for(i=0; i<n; i++){
		ans = ans * (i+1);
	}
	printf("%d\n", ans);
	return 0;

}

C++: #include<iostream>

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

int main(void){
    int n;
    std::cin>>n;
    std::cout<<factorial(n)<<std::endl;
    return 0;
}

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

using namespace std;

int main(void)
{
	int a;
	while(cin>>a)
	{
		int i=0,c=a;
		while(a!=1)c*=--a;
		cout<<c<<endl;
	}

	return 0;
}

C++: #include <iostream>
using namespace std;
 
int main() {
  int N;
  cin >> N;
  long long res = 1;
  for (auto i=1; i<=N; i++) {
    res *= i;
  }
  cout << res << endl;
}

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

int main(){
	long long int n, a = 1;

	cin >> n;
	for(int i=1 ; i<=n ; i++){
		a *= i;
	}
	cout << a << endl;
}

C++: #include <iostream>
using namespace std;
int main()
{int i,j;
long long mul;
bool stop=false;
do{cin>>i;
if(i>0 && i<=20){mul=1;
for (j=i;j>1;j--){mul*=j;}
cout<<mul<<endl;}
else if (i==0)cout<<"1"<<endl;
else if (i<0)
cout<<"Error."<<endl;
}while(stop==false);

return 0;}

C++: #include <stdio.h>
int dp[100];
int kai(int i){
		if(i==1||i==0){
			return 1;
		}
		return i*kai(i-1);
	}
int main(){

	int n;
	scanf("%d",&n);

	printf("%d\n",kai(n));
	return 0;

}

C++: 
#include <iostream>
using namespace std;
int main(){
    double ans[20];
    int i,n;
    cin>>n;
    for(i=0;i<=n;i++){
        if(i==0){
            ans[0]=1;
        }else{
            ans[i]=ans[i-1]*i;
        }
    }
    cout<<ans[n]<<endl;
    return 0;
}

C++: #include<iostream>
#include<string>
#include<vector>
#include<utility>
#include<queue>
#include<algorithm>
#include<cmath>
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<complex>
#define INF 1e9
#define llINF 9223372036854775807
#define pb push_back
#define mp make_pair 
#define F first
#define S second
#define ll long long

using namespace std;
int main(){
  int n;cin>>n;
  ll ans=1;
  for(int i=1;i<=n;i++)ans*=i;
  cout<<ans<<endl;
  return 0;
}