C#

    int n = Convert.ToInt32(Console.ReadLine().Trim());
    int count = 0;
    int max = 0;

    var bin = Convert.ToString(n, 2);

    for(int number = 0; number < bin.Length; number++)
    {
        if(bin[number] == '1')
        {
            count++;
        }
        else
        {
            count = 0;
        }

        if(count > max) max = count;
    }

    Console.WriteLine(max);