#include<stdio.h>
int main()
{
	long long int x, n;
	scanf("%lld %lld", &x, &n);
	long long int min, mid, max, o = 1, ans;
	if (x > 0)
	{
		o = -1;
		x *= -1;
	}
	min = -1;
	max = 2e9;
	while (max - min > 1)
	{
		mid = (max + min) / 2;
		if (mid * (mid + 1) / 2 + x > 0)
			max = mid;
		else
			min = mid;
	}
	if (n < max)
		ans = x + n * (n + 1) / 2;
	else if ((n - max) % 2 > 0)
		ans = x + min * (min + 1) / 2 - (n - min) / 2;
	else
		ans = x + max * (max + 1) / 2 + (n - max) / 2;
	ans *= o;
	printf("%lld\n", ans);
	return 0;
}