using System;

public class Program

{

    const string TAG = "tag";

    public static void Main()

    {

        var str = "some text with tag";

        if( str.Contains(TAG))

        {

            str = str.Replace(TAG, string.Empty);

        }

        log(str);

    }

    public static void log(object o) { Console.WriteLine(o == null ? "null" : o.ToString()); }

}