#!/usr/bin/env python3


def main():
    n, c = (int(x) for x in input().split())

    # We construct a DP table. Each index [i,j] represents the cost of finding
    # the boundary in that interval (including edges). We want to find the best
    # point to query. When querying we either get True or False. If we get True
    # we just found a non-strict upper bound for the boundary so the query costs
    # that index. If we get False we found a strict lower bound and the query
    # costs c. We want to consider the worst case so pick the maximum of the
    # two. We never need to query the nth index because it is guaranteed to be
    # True.
    dp = [[0] * n for _ in range(n)]

    for i in range(n):
        dp[i][i] = i + 1

    for i in reversed(range(n)):
        for j in range(i + 1, n):
            dp[i][j] = min(
                max(
                    # Too low (impossible if k = j because there is always a
                    # valid value)
                    dp[k + 1][j] + c if k < j else -1,
                    # Too high
                    dp[i][k - 1] + k + 1,
                    # Correct guess
                    dp[k][k],
                )
                for k in range(i, j + 1)
            )

    print(dp[0][-1])


if __name__ == "__main__":
    main()