from collections import defaultdict, Counter, deque
from itertools import groupby, accumulate, combinations, permutations, product, combinations_with_replacement
from bisect import bisect_left, bisect_right
from operator import itemgetter
import math
from heapq import heapify, heappush, heappop

LMI=lambda:list(map(int, input().split()))
LMS=lambda:list(map(str, input().split()))
MI=lambda:map(int, input().split())
MS=lambda:map(str, input().split())
II=lambda:int(input())
IS=lambda:input().split()
LI=lambda:list(input())

X,N=MI()
minus=False
if X<0:
    minus=True
X=abs(X)
# def calc(x, n):
#     tmp=n*(n + 1)//2  

#     if x<=0:
#         if x+tmp<=0:
#             return x + tmp
#         else:
#             y=(x + tmp)//2
#             return (x + tmp)-2*y
#     else:
#         if x - tmp > 0:
#             return x - tmp
#         else:
#             y=(-x + tmp)//2
#             return (x - tmp) + 2*y

#OK、NGを判断するための関数
def cond(X, N):
    return X >= N*(N+1)//2

ok, ng = 0, 10**18+1

#okとngの値が連番になるまで繰り返す
while abs(ok - ng)>1:
		#真ん中の値を計算
    mi = (ok + ng) // 2
    #条件判断の関数を使う
    if cond(X, mi):
    #okなら真ん中の値をokにし狭める
        ok = mi
    else:
    #ngなら真ん中の値をngにし狭める
        ng = mi
if ok>N:
    print(X - N*(N + 1)//2)
    exit()
else:
    cnt=N-ok
    now=X-ok*(ok + 1)//2
    if cnt%2==0:
        if minus:
            print(-1*(now+cnt//2))
        else:
            print(now+cnt//2)

    else:
        if minus:
            print(-1*(now-(ok+1)-(cnt-1)//2))
        else:
            print(now-(ok+1)-(cnt-1)//2)