/*
Main.cpp
Written By Namer_Mega ,Thanks for sharing your knowledge
*/#include <iostream>
using namespace std;
int factorial(int x)
{
int product = 1,k;
int sum = 0;
for(k = 1; k <= x ;k++)
{
product = product * k;
sum += product;
}
return sum;
}
int main()
{
cout<<factorial(20)<<endl;
return 0;
}