using System;

​

class Program

{

    static void Main()

    {

        var val = "";

        for (int i = 0; i < 10_000_000; i++)

        {

#if false//true

            val = string.Concat("string", 100, 100);

#elif true

            val = string.Concat("string", 100.ToString(), 100.ToString());

#endif

        }

        Console.WriteLine(val);

    }

}

​