import java.io.IOException;
import java.util.Scanner;

/**
 * //njudge compatible version
 */
public class main {

    public static void main(String[] args) throws IOException {
        Scanner io = new Scanner(System.in);
        int retekSzama = io.nextInt();
        int K = io.nextInt();
        int szabadRetek = 0;

        for (int i = 0; i < retekSzama; i++) {
            if (io.nextInt() == 1) szabadRetek++;
        }
        int N = szabadRetek-K+1;
        if (szabadRetek >= K) System.out.println((N)*(N+1)/2); //write the sum of all positive integers up to N (inclusive)
        else System.out.println(0);

        io.close();
    }
}