import re
def fun(s):
    try:
            username = s.split('@')[0]
            sec_part = s.split('@')[1]
            websitename = sec_part.split('.')[0]
            extension = sec_part.split('.')[1]
    except Exception:
        return False
    
    reg_username = r'^[a-zA-Z0-9_-]+$'
    reg_websitenane = r'^[a-zA-Z0-9]+$'
    reg_extension = r'^[a-zA-Z]{1,3}+$'


    if re.match(reg_username, username) is not None and re.match(reg_websitenane, websitename) is not None and re.match(reg_extension, extension) is not None:
        return True
    else:
        return False