import math
N, D = map(int, input().split())
print(math.ceil(N / (D + D + 1)))

c3359c30f59f90960c118e0fcddf8262e1500ff7
<mask token>

<mask token>
print(math.ceil(N / (D + D + 1)))

<mask token>
N, D = map(int, input().split())
print(math.ceil(N / (D + D + 1)))

import math
N, D = map(int, input().split())
print(math.ceil(N / (D + D + 1)))
