using System;

public class Program

{

    public static void Main()

    {

        var input = "110011001100";

        Console.WriteLine("Result: " + GetPeriod(input));

    }

    public static int GetPeriod(string input)

    {

        for (var i = 1; i <= input.Length / 2; i++)

        {

            var subString = input.Substring(0, i);

            var repeatedString = RepeatString(subString, input.Length);

            if (input.StartsWith(repeatedString))

                return i;

        }   

        return -1;

    }

    public static string RepeatString(string input, int length) 

    {

        var ret = "";

        int times = (length / input.Length) + 1;

        for (var i = 0; i < times; i++)

        {

            ret += input;

        }

        return ret.Substring(0, length);

    }

}