how to transfer Yahoo mails to Gmail

[lisa]

Guys I used to be on yahoo for emailing. but that was years ago and I adapted using Gmail which was better solution for my use. Now the problem is that I have many old mails lying in my yahoo account and they are very important. I dont want to loose them but everytime when I need to check them, I have to login to my yahoo account.

I want to know if there is any way which I can use to transfer my yahoo mails to gmail?