import java.util.Scanner;

class Factorial {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int[] inputArray = new int[100];
        int i = 0, input, temp = 0;

        do {
            System.out.print("Enter positive number (or 0) or negative number to end input : ");
            input = scanner.nextInt();
            inputArray[i] = input;
            i++;
        } while(input >= 0);

        do {
            System.out.println(inputArray[temp] + " factorial is " + inputArray[temp] + "! = " + factorial(inputArray[temp]) + "\n\n");
            temp++;
        } while(temp <= i);
    }

    public static int factorial(int n) {
        if (n < 0) {
            System.out.println("Negative numbers do not have factorials!");
            System.exit(0);
        }

        if (n == 0 || n == 1) return 1;

        return n * factorial(n-1);
    }
}