/* -*- coding: utf-8 -*-
 *
 * 3048.cc:  No.3048 Swing - yukicoder
 */

#include<cstdio>
#include<algorithm>

using namespace std;

/* typedef */

using ll = long long;

/* subroutines */

inline ll sigma(ll n) { return n * (n + 1) / 2; }

/* main */

int main() {
  ll x, n;
  scanf("%lld%lld", &x, &n);

  ll m;
  if (x > 0) {
    ll m0 = 0, m1 = 2000000000;
    while (m0 + 1 < m1) {
      ll m = (m0 + m1) / 2;
      if (sigma(m) < x) m0 = m;
      else m1 = m;
    }

    m = min(n, m0);
    x -= sigma(m);
  }
  else {
    ll m0 = 0, m1 = 2000000000;
    while (m0 + 1 < m1) {
      ll m = (m0 + m1) / 2;
      if (sigma(m) <= -x) m0 = m;
      else m1 = m;
    }
    m = min(n, m1);
    x += sigma(m);
  }
  //printf(" x=%lld, m=%lld\n", x, m);

  ll d = (n - m) / 2;
  x += d;
  m += d * 2;
  if (m < n) x -= n;

  printf("%lld\n", x);
  
  return 0;
}