First do-while loop not functioning properly

There seems to be something with my code. My code detects non-integers and keep asking the user to input a positive #, but when you insert a negative #, it just ask the user to input a positive just once. What is wrong? Something with my do-while loop for sure. I'm just focusing on the firstN, then I could do the secondN.

import java.util.Scanner;

public class scratch {

public static void main(String[] args) {

    Scanner input = new Scanner(System.in);

    int firstN = 0;
    int secondN = 0;
    boolean isNumber = false;
    boolean isNumPos = false;

    System.out.print("Enter a positive integer: ");

    do {
        if (input.hasNextInt()) {
            firstN = input.nextInt();
            isNumber = true;
        }
        if (firstN > 0) {
            isNumPos = true;
            isNumber = true;
            break;
        } else { 
            isNumPos = false;
            isNumber = false;
            System.out.print("Please enter a positive integer: ");
            input.next();
            continue;

        }

    } while (!(isNumber) || !(isNumPos));

    System.out.print("Enter another positive integer: ");
    do {
        if (input.hasNextInt()) {
            secondN = input.nextInt();
            isNumber = true;
        }
        if (secondN > 0) {
            isNumPos = true;
            isNumber = true;
        } else {
            isNumPos = false;
            isNumber = false;
            System.out.print("Please enter a positive integer: ");
            input.next();
        }

    } while (!(isNumber) || !(isNumPos));

    System.out.println("The GCD of " + firstN + " and " + secondN + " is " + gCd(firstN, secondN));

}

public static int gCd(int firstN, int secondN) {
    if (secondN == 0) {
        return firstN;
    } else
        return gCd(secondN, firstN % secondN);
}

}