internal class Program
{
    private static void Main(string[] args)
    {
        int k = int.Parse(Console.ReadLine().Split(' ')[1]);

        string[] input = Console.ReadLine().Split(' ');

        int count = 0;
        for (int i = 0; i < input.Length; i++) if (input[i] == "1") count++;
        int res = 0;
        for (int i = k; i <= count; i++) res += count - i + 1;

        Console.WriteLine(res);
    }
}