// factorial.ru
fn main()
{
  println!("factorial.ru running");
  let mut result = 0;
  println!("initial result= {}",result);
  result = factorial(0);
  println!("factorial(0)= {}",result);
  result = factorial(1);
  println!("factorial(2)= {}",result);
  result = factorial(2);
  println!("factorial(2)= {}",result);
  result = factorial(3);
  println!("factorial(3)= {}",result);
  result = factorial(10);
  println!("factorial(10)= {}",result);
  result = factorial(20);
  println!("factorial(20)= {}",result);
  // result = factorial(21);
  // println!("factorial(21)= {}",result);
  println!("overflow on factorial(21) error");
  println!("factorial.ru finished");
}

fn factorial(i: u64) -> u64 {
    match i {
        0 => 1,
        n => n * factorial(n-1)
    }
}