import re

def checkEMail(text):
    '''
    Function to check whether input is a valid EMail.

    Example:

    >>> checkEMail('someone@gmail.com')
    True
    >>> checkEMail('bill.gates@microsoft.com')
    True
    >>> checkEMail('.gates@sina.com')
    False
    >>> checkEMail('1_2@123.com.cn')
    True
    >>> checkEMail('foo@163.com1')
    False
    >>> checkEMail('foo#163.com')
    False

    '''
    if re.match(r'^([0-9a-zA-Z][0-9a-zA-Z\_\.]*)@([0-9a-z\-]+\.[a-z]{2,6}(\.[a-z]{2})*)$', text):
        return True
    return False

if __name__ == '__main__':
    import doctest
    doctest.testmod()

    while True:
        print("Please input an EMail(Ctrl+C to Exit):")
        m = input()
        if (checkEMail(m)):
            print("Valid.")
        else:
            print("Invalid")