using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine(StrStr("aaaaa","bba"));

    }

     public static int StrStr(string haystack, string needle) {

         if(haystack.Length == 0 || haystack == null) return -1;

         if(haystack.Equals(needle)) return 0;

         for(int i = 0; i<haystack.Length;i++){

            if (haystack[i]==needle[0] && (needle.Length<=haystack.Length-i)) {

                if (haystack.Substring(i, needle.Length)==needle) return i;

            }

         }

        return -1;

    }

}