import java.util.Scanner;

public class FactorialCalculator {

    public static void main(String[] args) {
        // Create a Scanner object for user input
        Scanner scanner = new Scanner(System.in);

        System.out.print("Enter a non-negative integer: ");
        
        // Validate user input
        if (!scanner.hasNextInt()) {
            System.out.println("Invalid input. Please enter a valid integer.");
            scanner.close();
            return;
        }

        int number = scanner.nextInt();

        // Check if the number is non-negative
        if (number < 0) {
            System.out.println("Factorial is not defined for negative numbers.");
        } else {
            // Calculate factorial
            long factorial = 1; // Use long to handle large results
            for (int i = 1; i <= number; i++) {
                factorial *= i;
            }

            // Display the result
            System.out.println("The factorial of " + number + " is: " + factorial);
        }

        // Close the scanner
        scanner.close();
    }
}