## https://yukicoder.me/problems/no/3048

import math

def main():
    X, N =  map(int, input().split())
    if X > 0:
        low = 1
        high = N
        if X - (high * (high + 1) )// 2 > 0:
            print(X - (N * (N + 1)) // 2)
            return

        while high - low > 1:
            mid =( high + low) // 2
            if X - (mid * (mid + 1)) // 2 <= 0:
                high = mid
            else:
                low = mid
        if X - (low * (low + 1)) // 2 <= 0:
            v = low
        else:
            v = high
        y = X - (v * (v + 1)) // 2
        p = (N - v + 1) // 2
        p0 = p * v + p ** 2
        m = (N - v) // 2
        m0 = m * v + m * (m + 1)
        ans = y + p0 - m0
    else:
        low = 1
        high = N
        if X + (high * (high + 1)) // 2 <= 0:
            print(X + (N * (N + 1)) // 2)
            return

        while high - low > 1:
            mid =( high + low) // 2
            if X + (mid * (mid + 1)) // 2 > 0:
                high = mid
            else:
                low = mid
        if X + (low * (low + 1)) // 2 > 0:
            v = low
        else:
            v = high
        
        y = X + (v * (v + 1)) // 2
        p = (N - v + 1) // 2
        p0 = p * v + p ** 2
        m = (N - v) // 2
        m0 = m * v + m * (m + 1)
        ans = y - p0 + m0        
    print(ans)







if __name__ == "__main__":
    main()