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



if n%(2*d + 1) == 0:

    print((n//(2*d + 1)))

else:

    print((n//(2*d + 1) + 1))
import math

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

print((math.ceil(n/(d*2+1))))
n, d = list(map(int, input().split()))
if n % (2 * d + 1) == 0:
    print((n // (2 * d + 1)))
else:
    print((n // (2 * d + 1) + 1))

import math

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

+import math + -if n % (2 * d + 1) == 0: -    print((n // (2 * d + 1))) -else: -    print((n // (2 * d + 1) + 1)) +print((math.ceil(n / (d * 2 + 1))))