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

public class Test {
    public static void main(String[] args) {
        String str ="${time}";
        String req="\\$\\{([a-z]{4})\\}";
        Pattern pattern=Pattern.compile(req);
        Matcher m=pattern.matcher(str);
        
        boolean s=m.find();
        if (s) {
            String c = m.group(1);
            System.out.println(c);
        } else {
            System.out.println("Not found.");
        }
    }
}