# input
import sys
input = sys.stdin.readline
II = lambda : int(input())
MI = lambda : map(int, input().split())
LI = lambda : [int(a) for a in input().split()]
SI = lambda : input().rstrip()
LLI = lambda n : [[int(a) for a in input().split()] for _ in range(n)]
LSI = lambda n : [input().rstrip() for _ in range(n)]
MI_1 = lambda : map(lambda x:int(x)-1, input().split())
LI_1 = lambda : [int(a)-1 for a in input().split()]

def graph(n:int, m:int, dir:bool=False, index:int=-1) -> list[set[int]]:
    edge = [[] for i in range(n+1+index)]
    for _ in range(m):
        a,b = map(int, input().split())
        a += index
        b += index
        edge[a].append(b)
        if not dir:
            edge[b].append(a)
    return edge

def graph_w(n:int, m:int, dir:bool=False, index:int=-1) -> list[set[tuple]]:
    edge = [set() for i in range(n+1+index)]
    for _ in range(m):
        a,b,c = map(int, input().split())
        a += index
        b += index
        edge[a].add((b,c))
        if not dir:
            edge[b].add((a,c))
    return edge

mod = 998244353
inf = 1001001001001001001
ordalp = lambda s : ord(s)-65 if s.isupper() else ord(s)-97
ordallalp = lambda s : ord(s)-39 if s.isupper() else ord(s)-97
yes = lambda : print("Yes")
no = lambda : print("No")
yn = lambda flag : print("Yes" if flag else "No")
def acc(a:list[int]):
    sa = [0]*(len(a)+1)
    for i in range(len(a)):
        sa[i+1] = a[i] + sa[i]
    return sa

prinf = lambda ans : print(ans if ans < 1000001001001001001 else -1)
alplow = "abcdefghijklmnopqrstuvwxyz"
alpup = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
alpall = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
URDL = {'U':(-1,0), 'R':(0,1), 'D':(1,0), 'L':(0,-1)}
DIR_4 = [[-1,0],[0,1],[1,0],[0,-1]]
DIR_8 = [[-1,0],[-1,1],[0,1],[1,1],[1,0],[1,-1],[0,-1],[-1,-1]]
DIR_BISHOP = [[-1,1],[1,1],[1,-1],[-1,-1]]
prime60 = [2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59]
sys.set_int_max_str_digits(0)
# sys.setrecursionlimit(10**6)
# import pypyjit
# pypyjit.set_param('max_unroll_recursion=-1')

from collections import defaultdict,deque
from heapq import heappop,heappush
from bisect import bisect_left,bisect_right
DD = defaultdict
BSL = bisect_left
BSR = bisect_right

from math import isqrt

x,n = MI()

if x > 0:
    t = isqrt(2*x)
    if n <= t:
        x -= n * (n+1) //2
        print(x)
        exit()

    x -= t * (t+1) // 2 # tまで処理  
    if x <= 0:
        x += t + 1
        t += 1
elif x <= 0:
    t = isqrt(2*(-x))
    if n <= t:
        x += n * (n+1) //2
        print(x)
        exit()
    
    x += t * (t+1) // 2 # tまで処理  
    if x <= 0:
        x += t + 1
        t += 1

# tまで処理している and 今は正
# これ以降 -(t+1) , +(t+2) をしばらく繰り返す

# 今は x、tまで処理
while t != n:
    if x + (n - t)//2 < n: #次に超すまでに終わりそう
        d = (n - t) // 2 #繰り返し回数
        t += 2 * d
        x += d
        # これが今のx
        if t != n:
            x -= n
        print(x)
        exit()
    
    y = 2 * x - t - 2 # このあたり
    
    t += (y - t) // 2
    t = y
    
    while True:
        x -= t+1
        t += 1
        if x > 0:
            x -= t+1
            t += 1
            x += t+1
            t += 1
            break
        else:
            x += t+1
            t += 1
print(x)