def lower_case_to_camel_case(s):
    """
    Convert a string from lower-case to camel-case.
    
    Example: 
    
        camel_case_to_lower_case('hello_world') == 'HelloWorld'
        
    """
    s = s.capitalize()
    while '_' in s:
        head, tail = s.split('_', 1)
        s = head + tail.capitalize()
    return s
