import math


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


def solve():
    a, b = input_split_line()
    Xes = [a]

    for i in range(1,b+1):
        if(Xes[i-1] <= 0):
            Xes.append(Xes[i-1] + i)
        else:
            Xes.append(Xes[i-1] - i)

    return Xes[-1]


print(solve())