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

def gcd(a, b):
	if b == 0: return a
	return gcd(b, a % b)

def solve(a1, m1, a2, m2):
	g = gcd(m1, m2)
	l = m1 / g * m2
	p, q = extgcd(m1, m2)
	if (a2 - a1) % g != 0:
		return (0, -1)
	p *= (a2 - a1) / g
	x = p * m1 + a1
	x %= l
	x += l
	x %= l
	return (x, l)

N = input()
X = [0] * N
Y = [0] * N
for i in xrange(N):
	X[i], Y[i] = map(int, raw_input().split())

for i in xrange(1, N):
	X[0], Y[0] = solve(X[0], Y[0], X[i], Y[i])
	if Y[0] == -1:
		print -1
		exit()

if X[0] == 0:
	X[0] += Y[0]

MOD = 10 ** 9 + 7
print X[0] % MOD