i, d = map(int, input().split())
a = d * 2 + 1
print((i + a - 1) // a)

8e1d98b866e109b9b8c83086212181be07089fa9
<mask token>

<mask token>
print((i + a - 1) // a)

i, d = map(int, input().split())
a = d * 2 + 1
print((i + a - 1) // a)
