我应该如何在C＃中计算文件哈希值（md5和SHA1）

This is my first C# project and I'm almost newbie. I use openfiledialoge for selecting file and get the filepath by GetFullPath method and store it in a variable called for example fpath. I need to calculate the hash of the file that its path is stored in fpath variable.I think it can be done via GetHashCode. Can anybody give me a snippet or a little guide?This is my first C# project and I'm almost newb