import sys

# sys.setrecursionlimit(200005)
# sys.set_int_max_str_digits(200005)
int1 = lambda x: int(x)-1
pDB = lambda *x: print(*x, end="\n", file=sys.stderr)
p2D = lambda x: print(*x, sep="\n", end="\n\n", file=sys.stderr)
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()

dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
# inf = -1-(-1 << 31)
inf = -1-(-1 << 62)

# md = 10**9+7
md = 998244353

from math import isqrt

x,n=LI()

if x<=0:
    l,r=0,-x
    while l+1<r:
        m=(l+r)//2
        if x+m*(m+1)//2>0:
            r=m
        else:
            l=m
    i=r
    now=x+i*(i+1)//2
    if n<=i:
        print(x+n*(n+1)//2)
    elif i&1==n&1:
        print(now+(n-i)//2)
    else:
        i+=1
        now-=i
        print(now-(n-i)//2)
else:
    l,r=0,x
    while l+1<r:
        m=(l+r)//2
        if x-m*(m+1)//2<=0:
            r=m
        else:
            l=m
    i=r
    now=x-i*(i+1)//2
    if n<=i:
        print(x-n*(n+1)//2)
    elif i&1==n&1:
        print(now-(n-i)//2)
    else:
        i+=1
        now+=i
        print(now+(n-i)//2)