def solve():
    L, K = map(int, input().split())

    top = 10**9 + 1
    btm = 0

    while top - btm > 1:
        mid = (top + btm) // 2

        if L - 2 * K * mid <= 0:
            top = mid
        else:
            btm = mid

    ans = btm * K
    print(ans)

if __name__ == '__main__':
    solve()