import java.util.Scanner;

public class Main {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		long x = sc.nextLong();
		long n = sc.nextLong();
		sc.close();

		long s = 1;
		if (x < 0) {
			x = -x;
			s = -1;
		}
		long ng = 2000000000;
		long ok = -1;
		while (Math.abs(ok - ng) > 1) {
			long mid = (ok + ng) / 2;
			long val = mid * (mid + 1) / 2;
			if (val < x) {
				ok = mid;
			} else {
				ng = mid;
			}
		}

		if (n <= ok) {
			long sub = n * (n + 1) / 2;
			x -= sub;
			System.out.println(x * s);
			return;
		}

		long sub = ok * (ok + 1) / 2;
		x -= sub;

		long n2 = n - ok;
		long v0 = x;
		long v1 = v0 - (ok + 1);

		long n21 = n2 / 2;
		long n22 = n2 % 2;
		if (n22 == 0) {
			v0 += n21;
			System.out.println(v0 * s);
		} else {
			v1 -= n21;
			System.out.println(v1 * s);
		}
	}
}