f=->x,y{return[x,1,0]if y==0
g,a,b=f[y,x%y]
[g,b,a-x/y*b]}
a=$<.drop(1).map{|e|e.split.map &:to_i}
p (r=a.reduce([0,1]){|(a,m),(b,n)|g,x,y=f[m,n]
v=(b-=a)/g
break if v*g!=b
l=m/g*n
[(a+v*x*m)%l,l]})?(r[0]==0?r[1]:r[0])%1000000007:-1