from fractions import gcd def inv(a, m): b, x, y = m, 1, 0 while b != 0: t = a // b a, b = b, a - t * b x, y = y, x - t * y pass return x % m def CRT(congs): x, m = 0, 1 for y, n in congs: g = gcd(m, n) if x % g != y % g: return -1, -1 m //= g; n *= m; m *= gcd(m, g); n //= m x %= m; x += (y - x % n + n) * inv(m, n) % n * m; m *= n pass return x, m mod = 10 ** 9 + 7 n = input() congs = [map(int, raw_input().split()) for _ in xrange(n)] ans = CRT(congs)[0] print -1 if ans == -1 else ans % mod