using System;

​

public class Program

{

    public static void Main()

    {

        const string input = "a=1,b=2,c=f1,d=f2";

        Console.WriteLine(input);

        var s1 = input.Split(',');

        string result = string.Empty;

        for (int i = 0; i < s1.Length/2; i++)

        {

            var a = s1[i*2].Split('=');

            var b = s1[i*2+1].Split('=');

            result+=string.Format("{0}={1}, {2}={3}, ", a[0], b[1], b[0], a[1]);

        }

        result = result.Remove(result.Length - 2, 2);

        Console.WriteLine(result);

    }

​

}