import math

L, K = map(int, input().split())

eat_times = int(math.ceil(L / K))
y_times = 0
h_times = 0
if eat_times % 2 == 0:
    y_times = int((eat_times - 2) / 2)
    h_times = y_times + 2
else:
    y_times = int((eat_times - 1) / 2)
    h_times = y_times + 1

print(K * y_times)