#!/usr/bin/ruby
def egcd(x,y)
	return [x,1,0] if y==0
	g,a,b=egcd(y,x%y)
	[g,b,a-x/y*b]
end
def chinese(a)
	return nil if !a||a.empty?
	a.reduce([0,1]){|(a1,m1),(a2,m2)|
		g,x,y=egcd(m1,m2)
		v=(a2-a1)/g
		break if v*g!=a2-a1
		lcm=m1/g*m2
		[(a1+v*x*m1)%lcm,lcm]
	}
end
r=chinese($<.drop(1).map{|e|e.split.map &:to_i})
p r ? r[0]%1000000007 : -1