index_of_last_zero

namespace index_of_last_zero
{
    internal class Program
    {
        static void Main(string[] args)
        {
            string input = Console.ReadLine();

            int indexOfLastZero = GetIndexOfLastZero(input);

            Console.WriteLine(indexOfLastZero);
        }

        private static int GetIndexOfLastZero(string input)
        {
            int l = 0, r = input.Length - 1;
            int retrunValue = -1;

            while (l <= r)
            {
                int m = (l + r) / 2;

                if (input[m] == '0' && m < input.Length - 1 && input[m + 1] == '1')
                {
                    return m;
                }

                if (input[m] == '0')
                {
                    l = m + 1;
                    retrunValue = input.Length - 1;
                }
                else
                {
                    r = m - 1;
                }
            }

            return retrunValue;
        }

    }
}