r, x, y, x_n, y_n = map(int, raw_input().split())

dist = ((x_n-x)**2 + (y_n-y)**2)**0.5

#print dist
#print dist/(2*r)
n = int(dist/(2*r))
additional = dist%(2*r)

if (additional > 0):
    n+=1
print n
