#!/usr/bin/env python3


def ans(low, high):
    if low > high: return 0
    if low == high: return high
    if (low, high) not in cache:
        cache[(low, high)] = min(
            max(
                guess + ans(low, guess - 1),
                c + ans(guess + 1, high) if guess < high else guess
            )
            for guess in range(low, high + 1)
        )
    return cache[(low, high)]


(n, c), cache = map(int, input().split()), {}
print(ans(1, n))