from math import gcd

def extgcd(a, b, x1=1, y1=0, x2=0, y2=1):
    if b == 0:
        return a, x1, y1
    q = a//b
    return extgcd(b, a%b, x2 ,y2, x1-x2*q, y1-y2*q)


def garner(b, m):
    x = 0
    mm = 1
    for i in range(len(m)):
        _, imm, _ = extgcd(mm, m[i])
        x += mm*(imm*(b[i]-x)%m[i])
        mm *= m[i]
    return x, mm

def pre_garner(b, m):
    for i in range(len(m)):
        for j in range(len(m)):
            if i == j:
                continue
            g = gcd(m[i], m[j])
            if (b[i]-b[j])%g != 0:
                return False
            m[i] //= g
            m[j] //= g
            gi = gcd(g, m[i])
            gj = g//gi
            while g != 1:
                g = gcd(gi, gj)
                gi *= g
                gj //= g
            m[i] *= gi
            m[j] *= gj
            b[i] %= m[i]
            b[j] %= m[j]
    return True

n = int(input())
b, m = zip(*(tuple(map(int, input().split())) for _ in range(n)))
b, m = list(b), list(m)
if not pre_garner(b, m):
    print(-1)
else:
    x, mm = garner(b, m)
    if all(bi==0 for bi in b):
        print(mm)
    else:
        print(x%(10**9+7))