# coding:utf-8

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

haruka_K = K
yuu_K = K

nokori_L = L

K_cnt = L // (haruka_K + yuu_K)
nokori_L = L % (haruka_K + yuu_K)
if L <= 2 * K:
    print(0)
else:
    print(yuu_K * K_cnt)