03. Sum Prime Non Prime

import java.util.Scanner;
public class SumPrimeNonPrime {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        long sumPrimeNumbers = 0;
        long sumNonPrimeNumbers = 0;
        String input = scanner.nextLine();
        while (!input.equals("stop")) {
            int number = Integer.parseInt(input);
            if (number < 0) {
                System.out.println("Number is negative.");
            } else {
                if (isPrime(number)) {
                    sumPrimeNumbers += number;
                } else {
                    sumNonPrimeNumbers += number;
                }
            }
            input = scanner.nextLine();
        }
        System.out.println("Sum of all prime numbers is: " + sumPrimeNumbers);
        System.out.println("Sum of all non prime numbers is: " + sumNonPrimeNumbers);
    }
    private static boolean isPrime(int num) {
        boolean isPrime = true;
        if (num < 2) isPrime = false;
        else {
            for (int i = 2; i <= Math.sqrt(num); i++) {
                if (num % i == 0) {
                    isPrime = false;
                    break;
                }
            }
        }
        return isPrime;
    }
}