import java.io.*;

public class Sums {

    public static void sum(BufferedReader in) {

	int s, nextInt;
	s = 0;
        nextInt = 1;

	System.out.println("Please input the sequence of integers to sum, terminated by a 0");

	while(nextInt!=0) {
            try{ nextInt = Integer.parseInt(in.readLine());
                        //Read next datum in input. An integer is expected
	    s = s + nextInt;
            } catch (NumberFormatException e) {
		System.out.println("Invalid number. Please reenter.");
            } catch (IOException e) {
		System.out.println("Invalid number. Please reenter.");
            }
	}

        System.out.println("The sum is " + s);
    }

    public static void main(String[] arg) {   
      	    
        BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
                         //"in" will receive data from the standard input stream

	String c;
	boolean moreSums = true;

	System.out.println("Do you wish to calculate a sum? (y/n)");

	while (moreSums) {
	    try{
		c = in.readLine(); 
	          //Read next datum in input. A string "y" or "n" is expected

		while (!c.equals("y") && !c.equals("n")) {
		    System.out.println("Please input y or n");
		    c = in.readLine();
		    }

		    if (c.equals("y")) {
			sum(in);
			System.out.println("Do you wish to calculate another sum? (y/n)");
		    } else 
			moreSums = false;

	    } catch (IOException e) {
		    System.out.println("Input error occurred. Please reenter.");
		}
	}

        System.out.println("Goodbye");
    }
}