import math
input = map(int, raw_input().split())

raio = input[0]
x = input[1]
y = input[2]
x1 = input[3]
y1 = input[4]

distance = (y1 - y)**2 + (x1 - x)**2
distance = distance**0.5

answer = distance/raio
print "%d" % math.ceil(answer/2.0)