import java.util.*;
import java.lang.*;
import java.io.*;
import java.io.*;
import java.util.stream.Collectors;
 
class Ideone
{
	public static void main(String[] args) {
        Map<String, String> map = new HashMap<>();
        map.put("Пупкин", "Василий");
        map.put("Иванов", "Василий");
        map.put("Пушкин", "Александр");
 
        map.keySet().stream()
        	.collect(Collectors.groupingBy(map::get)).entrySet().stream()
        		.filter(e -> e.getValue().size() > 1)
        		.flatMap(e -> e.getValue().stream())
        		.forEach(map::remove);
        System.out.println(map);
    }
}

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