Right, in your example, I believe you want st.Substring(11,4); But for a more useful approach, try this:
string st = "savi-server\test";
return st.Substring(st.IndexOf("\") + 1);
Try that first; essentially, it will start from the first t, and take the rest of the line. You may not need the +1, so if that doesn't work, try removing the +1.