n = int(raw_input())

def extgcd(x,y):
  if y == 0: return (x,1,0)
  g,a,b = extgcd(y,x%y);
  return (g,b,a-x//y*b)

def fail():
  print -1
  exit(0)

a = 0
b = 1
for i in xrange(n):
  na,nb = map(int,raw_input().split())
  g,x,y = extgcd(b,nb)
  if a%g != na%g: fail()
  l = b/g*nb
  a,b = ((a+(na-a)/g*x*b)%l,l)

if a == 0: a = b
print a%1000000007