import typing

def inv_gcd(a: int, b: int) -> typing.Tuple[int, int]:
	a %= b
	if a == 0:
		return (b, 0)
	s = b
	t = a
	m0 = 0
	m1 = 1
	while t:
		u = s // t
		s -= t * u
		m0 -= m1 * u
		s, t = t, s
		m0, m1 = m1, m0
	if m0 < 0:
		m0 += b // s
	return (s, m0)

def inv_mod(x: int, m: int) -> int:
	z = inv_gcd(x, m)
	return z[1]

def crt(r: typing.List[int], m: typing.List[int]) -> typing.Tuple[int, int]:
	r0 = 0
	m0 = 1
	for r1, m1 in zip(r, m):
		r1 %= m1
		if m0 < m1:
			r0, r1 = r1, r0
			m0, m1 = m1, m0
		if m0 % m1 == 0:
			if r0 % m1 != r1:
				return (0, 0)
			continue
		g, im = inv_gcd(m0, m1)
		u1 = m1 // g
		if (r1 - r0) % g:
			return (0, 0)
		x = (r1 - r0) // g % u1 * im % u1
		r0 += x * m0
		m0 *= u1
		if r0 < 0:r0 += m0
	return (r0, m0)


n = int(input())
e = int(input())
# x^2 + y 5^e - n = 0 has integer solution ?
# e = 0 -> ok.
if e == 0:
	print(0)
	exit()

# e > 0 -> n = 1, 4 mod 5 and n != mod 5^e
if not(n % 5 == 1 or n % 5 == 4 or n % (5**e) == 0):
	print("NaN")
	exit()

if n % (5**e) == 0:
	print(0)
else:
	# e = 1
	# x^2 - n = 0 (mod 5)
	a = -1
	for i in range(5):
		if (i * i - n) % 5 == 0:
			a = i
			break
	
	assert a >= 0

	# e = 2, 3, ..., 
	for t in range(2, e+1):
		c = (a * a - n) // (5 ** (t-1))
		y = -1
		for yy in range(5):
			if (2 * a * yy + c) % 5 == 0:
				y = yy
				break
		assert y >= 0
		b = (a + 5 ** (t-1) * y) % (5 ** t)
		a = b
	
	if a >= 2 ** 29:
		a -= 5 ** e
	
	print(a)