#include <iostream>
using namespace std;
#include <boost/multiprecision/cpp_int.hpp>
typedef boost::multiprecision::cpp_int bint;
const long long linf = 4610000000000000000;
int main()
{
  bint x, n;
  cin >> x >> n;
  if (0 < x)
  {
    bint l = 0, r = n+1;
    while (abs(l - r) > 1)
    {
      bint c = (l + r) / 2;
      if (x - c * (c+1) / 2 > 0)
      {
        l = c;
      }
      else
      {
        r = c;
      }
    }
    if (n <= l)
    {
      cout << x - n * (n+1) / 2 << '\n';
    }
    else
    {
      bint ans = x - l * (l+1) / 2;
      ans += (n - l) / 2;
      if ((n - l) % 2 == 1)
      {
        ans -= n;
      }
      cout << ans << '\n';
    }
  }
  else
  {
    bint l = 0, r = n+1;
    while (abs(l - r) > 1)
    {
      bint c = (l + r) / 2;
      if (x + c * (c+1) / 2 <= 0)
      {
        l = c;
      }
      else
      {
        r = c;
      }
    }
    if (n <= l)
    {
      cout << x + n * (n+1) / 2 << '\n';
    }
    else
    {
      bint ans = x + l * (l+1) / 2;
      ans -= (n - l) / 2;
      if ((n - l) % 2 == 1)
      {
        ans += n;
      }
      cout << ans << '\n';
    }
  }
  
  return 0;
}
/*
  File : ~/yukicoder/526/A.cpp
  Date : 2025/03/07
  Time : 21:02:05
*/