r, x, y, nx, ny = [int(x) for x in raw_input().split(' ')]
dist = ( ( ( (ny - y)**2) + ( (nx - x)**2) ) ** (0.5) )
if (dist % (2*r) == 0):
    print int( dist / (2*r) )
else:
    print int( dist / (2*r) ) + 1