using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        Regex appPathMatcher = new Regex(@"(?<!fil)([A-Za-z]:)?[\\\/\/]+[\S\s]*?(?=[\\\/\/]+bin)");

        string pathWindows = appPathMatcher.Match("c:\\app\\bin").Value;

        string pathLinux = appPathMatcher.Match("/app/bin").Value;

        string filename = pathWindows + "\\log4net.config";

        Console.WriteLine(pathWindows);

        Console.WriteLine(pathLinux);

        Console.WriteLine(filename);

    }

}