def fun(s):
    if '@' in s:
        list_c= s.split('@')
        if '.' in list_c[1]:
            list_c[1]=list_c[1].split('.')
            if list_c[1][1].isalpha() and len(list_c[1][1])<=3:
                if list_c[1][0].isalnum():
                    if list_c[0].replace('-','').replace('_','').isalnum():
                        return True
    return False