using System;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        string data = "%B3%F3%C7%F9";

        byte[] bData = new byte[data.Length / 3];

        for (int i = 0; i < data.Length; i += 3)

        {

            int pos = i / 3;            

            bData[pos] = Convert.ToByte(data.Substring(i + 1, 2), 16);

        }

        data = System.Text.Encoding.GetEncoding("euc-kr").GetString(bData);

        Console.WriteLine(data);

    }

}