Try to use Path.Combine(). This will return the path as a string.
s3 = System.IO.Path.Combine(IpA1[0].ToString() , p.ToString() , fileName);
It takes as many as arguments of the type string.
As OP is telling he is getting error, So below code will work for you.
s3 = System.IO.Path.Combine(System.IO.Path.Combine(IpA1[0].ToString() , p.ToString()) , fileName);