#include <iostream>
#include <vector>
#include <cstdio>
#include <sstream>
#include <map>
#include <string>
#include <algorithm>
#include <queue>
#include <cmath>

using namespace std;

typedef struct{
	int to;
	int cap;
	int rev;
}edge;

// node v : distance from s => level[v]
void bfs(vector<vector<edge> > &G, vector<int> &level, int s){
	fill(level.begin(), level.end(), -1);
	queue<int> q;
	q.push(s);
	level[s] = 0;
	while(!q.empty()){
		int e=q.front(); q.pop();
		for(int i=0; i<G[e].size(); i++){
			if(G[e][i].cap > 0 && level[G[e][i].to] < 0){
				level[G[e][i].to] = level[e] + 1;
				q.push(G[e][i].to);
			}
		}
	}
}

int dfs(vector<vector<edge> > &G, vector<int> &level, vector<bool> &used, vector<int> &iter, int s, int f,  int t){
	if(s==t) return f;
	else{
		//iter[e] : done searching from v[0] to v[ iter[e]-1 ]
		for(int &i=iter[s]; i<G[s].size(); i++){
			//distance from s to v[e][i].to must be longer than dist from s to v
			if(G[s][i].cap > 0 && level[s] < level[ G[s][i].to ]){
				int d = dfs(G, level, used, iter, G[s][i].to, min(f, G[s][i].cap), t);
				if(d>0){
					G[s][i].cap -= d;
					G[ G[s][i].to ][ G[s][i].rev ].cap += d;
					return d;
				}
			}
		}
		return 0;
	}
}

int dinic_maxflow(vector<vector<edge> > &G, int s, int t){
	const int INF = 100000000;
	int flow=0;
	while(true){
		vector<int> level(G.size(), -1);
		vector<int> iter(G.size(), 0);
		vector<bool> used(G.size(), false);
		bfs(G, level, s);
		if(level[t] < 0) return flow;	//unable to achieve to t
		while(true){
			int f = dfs(G, level, used, iter, s, INF, t);
			if(f==0) break;
			else flow += f;
		}
	}
}

void add_edge(vector<vector<edge> > &G, int from, int to, int cap){
	G[from].push_back((edge){to, cap, (int)G[to].size()});
	G[to].push_back((edge){from, 0, (int)G[from].size() - 1});
}

//わけわかめ
int main(){
	int N;
	cin >> N;
	vector<int> B(N);
	vector<int> C(N);
	for(int i=0; i<N; i++){
		cin >> B[i] >> C[i];
	}
	
	vector< vector<edge> > G(2*N+2);
	int s = 2*N;
	int t = 2*N+1;

	int M;
	cin >> M;
	vector<int> D(M);
	vector<int> E(M);
	vector<bool> valid(N, false);
	for(int i=0; i<M; i++){
		cin >> D[i] >> E[i];
		valid[ D[i] ] = true;
	}

	const int INF = 100000000;
	for(int i=0; i<N; i++){
		add_edge(G, s, i, B[i]);
		add_edge(G, i, N+i, INF);
		add_edge(G, N+i, t, C[i]);
	}
	
	for(int i=0; i<M; i++){
		add_edge(G, D[i], N+E[i], INF);
	}

	int ans = 0;
	for(int i=0; i<N; i++){
		ans += B[i] + C[i];
	}
	ans -= dinic_maxflow(G, s, t);
	
	cout << ans << endl;
	return 0;
}