JOptionPane - input dialog box program

Write a program that uses input dialog boxes to read three test marks, each out of 100. The program discards your lowest mark and shows the average of the two higher marks in a message dialog box.

This is how far i got and i dont know where to do from here, any help would be appreciated:

import javax.swing.JOptionPane; 

public class Average {

    public static void main (String [] args){

        String test1, test2, test3, avg;

        test1= JOptionPane.showInputDialog("Please input mark for test 1: ");

        test2= JOptionPane.showInputDialog("Please input mark for test 2: ");

        test3= JOptionPane.showInputDialog("Please input mark for test 3: ");

    }

}