def inverse(a, mod):
    '''
    a, mod が互いに素な場合modular逆数を返す
    '''
    assert mod > 0
    a %= mod
    p = mod
    x, y = 0, 1
    while a > 0:
        n = p // a
        p, a = a, p % a, 
        x, y = y, x - n * y
    return x % mod if p == 1 else -1

import math
def preprocess_garner(b, m, mod):
    n = len(m)
    assert len(b) == n
    for i in range(n):
        for j in range(i+1, n):
            g = math.gcd(m[i], m[j])
            if (b[i] - b[j]) % g != 0:
                return False
            m[i] //= g
            m[j] //= g
            gi = math.gcd(m[i], g)
            gj = g // gi
            while True:
                g = math.gcd(gi, gj)
                gi *= g
                gj //= g
                if g == 1:
                    break
            m[i] *= gi
            m[j] *= gj
            b[i] %= m[i]
            b[j] %= m[j]
    return True

def garner(b, m, mod):
    '''
    互いに素なmに対してall(x≡b[i](mod, m[i]))を満たす x と mの積を求める。
    多倍長整数を回避。O(n^2+nlogn)
    '''
    n = len(m)
    s = [0] * (n+1)
    p = [1] * (n+1)
    m.append(mod)
    for i in range(n):
        t = (b[i] - s[i]) * inverse(p[i], m[i]) % m[i]
        for j in range(i+1, n+1):
            s[j] = (s[j] + t * p[j]) % m[j]
            p[j] = p[j] * m[i] % m[j]
    m.pop()
    return s[-1], p[-1]

n = int(input())
x, y = [0] * n, [0] * n
for i in range(n):
    x[i], y[i] = map(int, input().split())
mod = 10**9+7
if not preprocess_garner(x, y, mod):
    print(-1)
    quit()
ans, _ = garner(x, y, mod)
print(ans)