why can't download file from linux server into local window disk c:?

[pengsir]

My vps ip is x.y.z.w ,i want to download /etc/passwd from linux server  
into my local window disk c: .

import paramiko
host = "x.y.z.w"
port = 22
transport = paramiko.Transport((host, port))
password = "mykey"
username = "root"
transport.connect(username = username, password = password)
sftp = paramiko.SFTPClient.from_transport(transport)
filepath = '/etc/passwd'
localpath = 'c:'
sftp.get(filepath, localpath)

Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
   File "D:\Python34\lib\site-packages\paramiko\sftp_client.py", line 
719, in get

     with open(localpath, 'wb') as fl:
PermissionError: [Errno 13] Permission denied: 'c:'