// This is only for printing the test cases - not used in the F method

using System;

​

Func<string,string> F = null;

F=a=>{int i=0,l;try{for(;;)l=(a+(a+a.Length).Length)[++i];}catch{}return a+i;};

​

Console.WriteLine(F("aaa"));

Console.WriteLine(F(""));

Console.WriteLine(F("aaaaaaaa"));

Console.WriteLine(F("aaaaaaaaa"));

Console.WriteLine(F("a1"));

Console.WriteLine(F("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"));

Console.WriteLine(F("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"));

​