N=int(input())
A,B=[],[]
for i in range(N):
  x,y=map(int, input().split())
  A.append(x)
  B.append(y)


def inv_gcd(a, b):
  a = a%b
  if a == 0:
    return b,0
  s = b
  t = a
  m0 = 0
  m1 = 1
  while t:
    u = s//t
    s -= t*u
    m0 -= m1*u
    s,t = t,s
    m0,m1 = m1,m0
  if m0 < 0:
    m0 += b//s
  return s,m0
 
def chinese_remainder(rrr, mmm):
  n = len(rrr)
  r0 = 0
  m0 = 1
  for i in range(n):
    r1 = rrr[i]%mmm[i]
    m1 = mmm[i]
    if m0 < m1:
      r0,r1 = r1,r0
      m0,m1 = m1,m0
    if m0%m1 == 0:
      if r0%m1 != r1:
        return 0,0
      continue
    g,im = inv_gcd(m0,m1)
    u1 = m1//g
    if (r1-r0)%g:
      return 0, 0
    x = (r1-r0)//g%u1*im%u1
    r0 += x*m0
    m0 *= u1
    if r0 < 0:
       r0 += m0
  return r0,m0
mod=10**9+7
r,m=chinese_remainder(A,B)
# r : 2*X+2*Yで割ってX+a余り、P+Qで割ってP+b余る　最小の数
# m : 2*X+2*YとP+Qの最小公倍数
if m==0:
  print(-1)
else:
  if r==0:
    r+=m
  print(r%mod)