阶乘

import java.util.Scanner;


public class 阶乘 {

public static int g(int n) {
if (n >= 0) {
if (n == 0) {
return 1;
} else {

return n * g(n - 1);

}
}

return -1;
}
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int m = sc.nextInt();
System.out.println(g(m));
}


}