'''
Created on 5 авг. 2015 г.

@author: alyaksei-pc
'''
from math import sqrt

def R(x1, y1, x2, y2):
    return sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1))

eps = 0.00000001;
r, x1, y1, x2, y2 = map(int, input().split())
ans = R(x1, y1, x2, y2) / r / 2 + (R(x1, y1, x2, y2) % (2*r) > eps)
print (round(ans))