"""

-10 , +10 , -11 , +11 , -12 

"""

import sys

x,n = map(int,input().split())

if x >= 0:

    l = 0
    r = n

    if x - ( (1+n)*n//2 ) >= 0:
        print ( x - ( (1+n)*n//2 ) )
        sys.exit()

    while r-l != 1:
        m = (l+r)//2
        if x - ( (1+m)*m//2 ) < 0:
            r = m
        else:
            l = m

    ans = x - ( (1+r)*r//2 )
    rem = n - r
    ans -= rem // 2

    if rem % 2 == 1:
        ans += n

    print (ans)

else:

    l = 0
    r = n

    if x + ( (1+n)*n//2 ) < 0:
        print ( x + ( (1+n)*n//2 ) )
        sys.exit()

    while r-l != 1:
        m = (l+r)//2
        if x + ( (1+m)*m//2 ) >= 0:
            r = m
        else:
            l = m

    ans = x + ( (1+r)*r//2 )
    rem = n - r
    ans += rem // 2

    if rem % 2 == 1:
        ans -= n

    print (ans)