f=->x,y{return[x,1,0]if y==0
g,a,b=f[y,x%y]
[g,b,a-x/y*b]}
gets
a=$<.map{|e|e.split.map &:to_i}
p (r=a.reduce{|(a,m),(b,n)|g,x,y=f[m,n]
(b-=a)%g>0&&break
n*=m/g
[(a+b/g*x*m)%n,n]})?r[r[0]>0?0:1]%(10**9+7):-1