import math

def input_split_line():
    return list(map(int, input().split()))

def solve():
    a, b = input_split_line()
    Xim1 = a

    for i in range(1,b+1):
        if(Xim1 <= 0):
            Xim1 += i
        else:
            Xim1 -= i
    return Xim1

print(solve())