import java.util.*;
import java.lang.*;
import java.io.*;
 
class MapKeys {
 
    public static void main(String a[]){
        TreeMap<String, String> hm = new TreeMap<String, String>();
        //add key-value pair to TreeMap
        hm.put("first", "FIRST INSERTED");
        hm.put("second", "SECOND INSERTED");
        hm.put("third","THIRD INSERTED");
        System.out.println(hm);
        Set<String> keys = hm.keySet();
        for(String key: keys){
            System.out.println(key);
        }
    }
}

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