import java.util.*;
import java.util.stream.*;
 
class Ideone {
	public static void main (String[] args) {
		Map<String, List<Integer>> values = new HashMap<>();
        values.put("a", Arrays.asList(4, 8, 9, 10)); // max value is 10
        values.put("b", Arrays.asList(20, 32, 1, 2)); // max value is 32
        values.put("c", Arrays.asList(11, 50, 20, 6)); // max value is 50
 
        Integer minMax = values.values().stream().map(Collections::max).collect(Collectors.minBy(Integer::compareTo)).get();
 
        System.out.println(minMax);
	}
}

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