import math
import re

str = raw_input()
par = re.findall("[-\d]+", str)
par = [int(elem) for elem in par]
r = par[0]
x = par[1]
y = par[2]
x1 = par[3]
y1 = par[4]

dist = math.sqrt(math.pow(x1-x, 2)+math.pow(y1-y, 2))
print int(math.ceil(dist/(2*r)))