import java.util.*; class Student { String name; String age; public Student(String name, String age) { this.name = name; this.age = age; } public String toString() { return name + ":" + age; } } public class test{ public static void main(String[] args) { Set set = new HashSet(); set.add(new Student("Tom", "10")); set.add(new Student("Jerry", "10")); set.add(new Student("Tom", "10")); System.out.println(set.size()); } }