x,n = map(int,input().split())
if x<=0:
    high = -x+1
    low = 0
    while high-low>1:
        mid = (high+low)//2
        if x+(mid*(mid+1))//2>0:
            high = mid
        else:
            low = mid
    k = high
    if n<k:
        ans = x+(n*(n+1))//2
    elif (n-k)%2==0:
        s = x+(k*(k+1))//2
        ans = s+(n-k)//2
    else:
        t = x+(k*(k+1))//2-(k+1)
        ans = t-(n-k)//2
else:
    high = x
    low = 0
    while high-low>1:
        mid = (high+low)//2
        if x-(mid*(mid+1))//2<=0:
            high = mid
        else:
            low = mid
    k = high
    if n<k:
        ans = x-(n*(n+1))//2
    elif (n-k)%2==0:
        s = x-(k*(k+1))//2
        ans = s-(n-k)//2
    else:
        t = x-(k*(k+1))//2+(k+1)
        ans = t+(n-k)//2
print(ans)