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, md):
    x = [0]*(len(b)+1)
    for i in range(len(b)):
        v = 0
        mm = rmm = 1
        for j in range(i):
            v += (mm * x[j+1]) % m[i]
            v %= m[i]
            mm *= m[j]
            mm %= m[i]
        rmm = extgcd(mm, m[i])[1]
        rmm %= m[i]
        x[i+1] = rmm * (b[i] - v)
        x[i+1] %= m[i]
    xx = 0
    mm = 1
    for i in range(len(b)):
        xx += mm*x[i+1]
        xx %= md
        mm *= m[i]
        mm %= md
    return xx, 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
md = 10**9+7
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, md)
    if all(bi==0 for bi in b):
        print(mm)
    else:
        print(x)