import math;
rr=raw_input();
rr=rr.split(" ");
rr=[int(dd) for dd in rr]
r=int(rr[0]);
d=math.sqrt(math.pow(rr[1]-rr[3],2)+math.pow(rr[2]-rr[4],2));
frac=d/(2*r);
if(math.ceil(frac)==d/(2*r)):
	print int(d/(2*r));
else:
	print int(d/(2*r))+1;
