import math
def distance(x1, y1, x2, y2):

    return math.sqrt(math.pow(x2 - x1, 2) +
                     math.pow(y2 - y1, 2) * 1.0)

r,x,y,x1,y1=map(int,input().split())
dis = distance(x, y, x1, y1)
print(math.ceil(dis/(2*r)))