import java.util.concurrent.ConcurrentHashMap;
import java.util.stream.IntStream;
import java.util.Map;

public class Test{
    
    public static void main(String [] args){
        final int size = 12; // or 24, 48, 96, 192...
        final Map<Integer, Integer> map = new ConcurrentHashMap<>();
        IntStream.range(1, size).forEach(i -> map.put(i, i));

        map.computeIfAbsent(size, k ->
        {
            map.computeIfAbsent(size + 1, k2 -> size + 1);
            return size;
        });
    }
}