#include <algorithm>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <functional>
#include <iostream>
#include <map>
#include <memory>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>
 
using namespace std;
 
#define sz size()
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define all(c) (c).begin(), (c).end()
#define rep(i,a,b) for(int i=(a);i<(b);++i)
#define clr(a, b) memset((a), (b) ,sizeof(a))
 
#define MOD 1000000009

#define NN 82
#define INF 100000000

int v[NN][NN];
int flag[NN];

int flow(int s, int e, int f){
  if(s == e)return f;

  flag[s] = 1;

  for(int i = 0; i < NN; i++){
    if(v[s][i] > 0 && flag[i] == 0){
      int d = flow(i, e, min(f, v[s][i]));
      if(d > 0){
        v[s][i] -= d;
        v[i][s] += d;
        return d;
      }
    }
  }
  return 0;
}

void ae(int from, int to, int cost){
  v[from][to] = cost;
}

int main(){
  clr(v,-1);
  int sum = 0;
  int n;
  cin >> n;
  rep(i,0,n){
    int b,c;
    cin >> b >> c;
    ae(2*n,i,b);
    ae(i+n,2*n+1,c);
    ae(i,i+n,INF);
    sum += b+c;
  }
  int m;
  cin >> m;
  rep(i,0,m){
    int d,e;
    cin >> d >> e;
    ae(d,e+n,INF);
    ae(e+n,d,INF);
  }
  int ans = 0;
  for(;;){
    memset(flag,0,sizeof(flag));
    int f = flow(2*n,2*n+1, INF);
    if(f == 0)break;
    ans += f;
  }
  cout << sum-ans << endl;
  return 0;
}