#include<bits/stdc++.h>

#define debug(x) cerr << #x << ": " << x << '\n'
#define debugArray(x,n) for(long long hoge = 0; (hoge) < (n); ++ (hoge)) cerr << #x << "[" << hoge << "]: " << x[hoge] << '\n'
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef vector<ll> vll;
const ll INF = LLONG_MAX/2;
const ll MOD = 1e9+7;


struct FordFulkerson {
    typedef long long flow_type;
    struct edge {
        int src, dst;
        flow_type capacity, flow;
        size_t rev;
    };
    int n;
    vector<vector<edge>> adj;
    FordFulkerson(int n) : n(n), adj(n) { }
    void add_edge(int src, int dst, flow_type capacity) {
        adj[src].push_back({src, dst, capacity, 0, adj[dst].size()});
        adj[dst].push_back({dst, src, 0, 0, adj[src].size()-1});
    }
    flow_type max_flow(int s, int t) {
        vector<bool> visited(n);
        function<flow_type(int,flow_type)> augment = [&](int u, flow_type cur) {
            if (u == t) return cur;
            visited[u] = true;
            for (auto &e: adj[u]) {
                if (!visited[e.dst] && e.capacity > e.flow) {
                    flow_type f = augment(e.dst, min(e.capacity - e.flow, cur));
                    if (f > 0) {
                        e.flow += f;
                        adj[e.dst][e.rev].flow -= f;
                        return f;
                    }
                }
            }
            return flow_type(0);
        };
        for (int u = 0; u < n; ++u)
            for (auto &e: adj[u]) e.flow = 0;

        flow_type flow = 0;
        while (1) {
            fill(visited.begin(),visited.end(), false);
            flow_type f = augment(s, INF);
            if (f == 0) break;
            flow += f;
        }
        return flow;
    }
    const vector<edge> operator[](const ll k){return adj[k];}
};

signed main(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  ll N;cin>>N;
  FordFulkerson g(2*N+2);
  ll src=2*N,dst=2*N+1;
  ll ans = 0;
  for(ll i=0;i<N;i++){
    ll B,C;cin>>B>>C;
    ans += B+C;
    g.add_edge(src,i,B);
    g.add_edge(i+N,dst,C);
  }
  ll M;cin>>M;
  for(ll i=0;i<M;i++){
    ll D,E;cin>>D>>E;
    g.add_edge(D,E+N,INF);
  }
  for(ll i=0;i<N;i++){
    g.add_edge(i,i+N,INF);
  }
  ans -= g.max_flow(src,dst);
  cout<<ans<<endl;
  return 0;
}