import math



n,d = list(map(int,input().split()))



r = 2 * d + 1



ans = math.ceil(n / r)



print(ans)
import math



n,d = list(map(int,input().split()))



print((math.ceil(n / (2*d+1))))

import math

n, d = list(map(int, input().split()))
r = 2 * d + 1
ans = math.ceil(n / r)
print(ans)

import math

n, d = list(map(int, input().split()))
print((math.ceil(n / (2 * d + 1))))

-r = 2 * d + 1 -ans = math.ceil(n / r) -print(ans) +print((math.ceil(n / (2 * d + 1))))