using System;

using System.Linq;

​

namespace ConsoleApp3

{

    public class Program

    {

        public static void Main(string[] args)

        {

            test("0000000000000"); // Outputs 0

            test("0000100010000"); // Outputs 3

            test("1111111111111"); // Outputs 0

            test("1000000000001"); // Outputs 11

            test("1000000000000"); // Outputs 0

            test("0000000000001"); // Outputs 0

            test("1010101010101"); // Outputs 1

            test("1001000100001"); // Outputs 4

        }

​

        static void test(string s)

        {

            Console.WriteLine(CountZerosBetweenOnes(s));

        }

​

        public static int CountZerosBetweenOnes(string binary)

        {

            var indicesOfOnes = 

                binary.Select((c, i) => new {c, i})

                .Where(x => x.c == '1')

                .Select(x => x.i);

​

            return 

                indicesOfOnes

                .Zip(indicesOfOnes.Skip(1), (a, b) => b - a - 1)

                .DefaultIfEmpty(0)

                .Max();

        }

    }

}

​