Programming Basic - Sum Prime Non Prime [Java]

import java.util.Scanner;

public class SumPrimeNonPrimeEx {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        String input = scan.nextLine();
        int sumPrime = 0;
        int sumNotPrime = 0;

        while (!input.equals("stop")) {
            int number = Integer.parseInt(scan.nextLine());
            int counter = 0;
            if ( number < 0) {
                System.out.println("Number is negative.");
            } else {
                for (int i = 1; i <= number ; i++) {
                    if (number % i == 0) {
                        counter++;
                    }
                }
                if (counter == 2) {
                    sumPrime += number;
                } else {
                    sumNotPrime += number;
                }
            }
            input = scan.nextLine();
        }
        System.out.printf("Sum of all prime numbers is: %d", sumPrime);
        System.out.printf("Sum of all non prime numbers is: %d", sumNotPrime);
    }
}