#include<iostream>
using namespace std;

int x(int n){

	int y=1;
	for(int i=1;i<=n;i++)
		y=y*i;
	return y;

}

int main(){
	int a,b=1;
	cout<<"请输入一个整数:";
	cin>>a;
	
	b=x(a);	
	cout<<b<<endl;
	return 0;
}