import java.util.Scanner;

public class Main { public static void main(String[] args) { Scanner scanner = new Scanner(System.in); long n = scanner.nextLong(); long fakt = 1;

    if (0 <= n && n <= 20) {
        while (n != 0) {
            fakt *= n;
            n--;
        }
        System.out.println(fakt);
    }
}

}