#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef pair<int,int> P;
#define REP(i,n) for(int i=0;i<int(n);i++)









int main(void){
	cin.tie(nullptr);  ios_base::sync_with_stdio(false);
	ll i,j;


	ll x,n;
	cin >> x >> n;



	if(x>0){

    ll ng=-1,ok=2000000000;
     while(ok-ng>1){

         ll m=(ok+ng)/2;

          if(x<=m*(m+1)/2) ok=m;
          else ng=m;

      }


      if(ok>=n){
    	  cout << x-n*(n+1)/2 << endl;
    	  return 0;
      }

      ll p=(n-ok)/2;
      x-=ok*(ok+1)/2;
      if((n-ok)%2==0){
    	  cout << x-p << endl;
    	  return 0;
      }else{
    	  cout << x-p+n << endl;
    	  return 0;
      }


	}else{

		x*=-1;

	    ll ng=-1,ok=2000000000;
	     while(ok-ng>1){

	         ll m=(ok+ng)/2;
	          if(x<=m*(m+1)/2) ok=m;
	          else ng=m;

	      }


	      x*=-1;
	      if(ok>=n){
	    	  cout << x+n*(n+1)/2 << endl;
	    	  return 0;
	      }


	      ll p=(n-ok)/2;
	      x+=ok*(ok+1)/2;

	      if(x==0){

	    	     if((n-ok)%2==0){
	    	    	  cout << x-p << endl;
	    	    	  return 0;
	    	      }else{
	    	    	  cout << x-p+n << endl;
	    	    	  return 0;
	    	      }

	      }else{


	      if((n-ok)%2==0){
	    	  cout << x+p << endl;
	    	  return 0;
	      }else{
	    	  cout << x+p-n << endl;
	    	  return 0;
	      }


	      }
	}





	return 0;
}