def ext_gcd(a, b):
  if b == 0:
    return (a, 1, 0)
  else:
    g, x, y = ext_gcd(b, a % b)
    return (g, y, x - (a // b) * y)

def chinese_rem(b1, m1, b2, m2):
  d, x, _ = ext_gcd(m1, m2)

  if (b2 - b1) % d != 0:
    return (None, None)
  else:
    m = m1 * (m2 // d)
    t = ((b2 - b1) // d * x) % (m2 // d)
    r = (b1 + m1 * t) % m
    return (r, m)

r, m = map(int, input().split())
for _ in range(2):
  x, y = map(int, input().split())
  nr, nm = chinese_rem(r, m, x, y)
  if nr is None:
    print("-1")
    exit()
  else:
    r, m = nr, nm

print(r)