z=9999
n=gets.to_i
l=n*5
g=(1..l).map{[0]*l}
a=0
(1..n).map{|u|b,c=gets.split;a+=g[1][2+u]=b.to_i;a+=g[r=2+n+u][2]=c.to_i;g[2+u][r]=z}
gets.to_i.times{d,e=gets.split;g[3+d.to_i][3+n+e.to_i]=z}
(
q=[1];p=[0]*l
(u=q.shift;l.times{|v|(p[v]=u;q<<v)if p[v]<1&&g[u][v]>0})while q.any?
break if p[v=w=2]<1
m=z
(m=[m,g[u=p[v]][v]].min;v=u)while v>1
a-=m
(g[u=p[w]][w]-=m;g[w][u]+=m;w=u)while w>1
)while !!n
p a