import java.util.regex.Matcher;
import java.util.regex.Pattern;


public class Camel_UnderlineConverter {
	public static String camel4underline(String param){
		Pattern  p=Pattern.compile("[A-Z]");
		if(param==null ||param.equals("")){
			return "";
		}
		StringBuilder builder=new StringBuilder(param);
		Matcher mc=p.matcher(param);
		int i=0;
		while(mc.find()){
			builder.replace(mc.start()+i, mc.end()+i, "_"+mc.group().toLowerCase());
			i++;
		}

		if('_' == builder.charAt(0)){
			builder.deleteCharAt(0);
		}
		return builder.toString();
	}
	public static String underline2camel(String param){
		Pattern  p=Pattern.compile("_[a-z]");
		if(param==null ||param.equals("")){
			return "";
		}
		StringBuilder builder=new StringBuilder(param);
		Matcher mc=p.matcher(param.toLowerCase());
		int i = 0;
		while(mc.find()){
			builder.replace(mc.start()-i, mc.end()-i, mc.group(0).substring(1).toUpperCase());
			i++;
		}

		return builder.toString();
	}
public static void main(String[] args) {
	System.out.println(underline2camel("SAY_HELLO_WORLD".toLowerCase()));
}
}