n=gets.to_i
l=n*4
g=(1..l).map{[0]*l}
a=0
(0...n).map{|u|
  b,c=gets.split
  a+=g[0][2+u]=b.to_i
  a+=g[2+n+u][1]=c.to_i
  g[2+u][2+n+u]=9999
}
gets.to_i.times{
  d,e=gets.split
  g[2+d.to_i][2+n+e.to_i]=9999
}
(
  q=[0]
  p=[-1]*l
  (
    u=q.shift
    l.times{|v|
      (
        p[v]=u
        q<<v
      )if p[v]<0&&g[u][v]>0
    }
  )while q.any?
  break if p[1]<0
  m=9999
  v=1
  (m=[m,g[u=p[v]][v]].min;v=u)while v>0
  a-=m
  v=1
  (g[u=p[v]][v]-=m;g[v][u]+=m;v=u)while v>0
)while !!n
p a