boolean IsExit = false и while (!isExit)

import java.util.Scanner;
public class whileaaaaaa {
    public static void main(String[] args) {
        Scanner nscan = new Scanner(System.in);
        int sum = 0;
        boolean isExit = false;

        while(!isExit){
            if(nscan.hasNextInt()){
                int x = nscan.nextInt();
                sum = sum + x;
            }else if (nscan.hasNextLine()){
                String fs = nscan.nextLine();
                if (fs.equals("ENTER"))
                    isExit = true;
            }
        }
        System.out.println(sum);
    }
}