def safe_base64_decode(s):
    s_len=len(s)
    num=4-(s_len%4)
    if num==4:
        num=0
    while num>0 :
        s=s+b'='
        num=num-1
    return base64.b64decode(s)


assert b'abcd' == safe_base64_decode(b'YWJjZA=='), safe_base64_decode('YWJjZA==')
assert b'abcd' == safe_base64_decode(b'YWJjZA'), safe_base64_decode('YWJjZA')
print('Pass')