#include <iostream>
#include <vector>
#include <cstring>
#include <string>
#include <algorithm>
#include <iomanip>
#include <cmath>
#include <cassert>
using namespace std;

typedef int Weight;
typedef int Capacity;
struct Edge {
	int src, dst; Capacity cap;
	Edge(int s, int d, Capacity c) : src(s), dst(d), cap(c) {}
};
typedef vector<Edge> Edges;
typedef vector<Edges> Graph;

struct Dinic {
	int n, s, t;
	vector<int> level, prog, que;
	vector<vector<Capacity> > cap, flow;
	vector<vector<int> > g;
	Capacity inf;
	Dinic() {}
	Dinic(const Graph &graph)
		: n(graph.size()),
		cap(n, vector<Capacity>(n)), flow(n, vector<Capacity>(n)),
		g(n, vector<int>()), inf((int)1e9) {
		for(int i = 0; i < n; i++) {
			for(int j = 0; j < graph[i].size(); j++) {
				const Edge& e = graph[i][j];
				int u = e.src, v = e.dst;
				Capacity c = e.cap;
				add_edge(u, v, c);
			}
		}
	}
	Dinic(int n_) : n(n_), cap(n, vector<Capacity>(n)), flow(n, vector<Capacity>(n)),
		g(n, vector<int>()), inf((int)1e9) {
	}
	void add_edge(int u, int v, Capacity c) {
		cap[u][v] += c; cap[v][u] += c; flow[v][u] += c;
		g[u].push_back(v); g[v].push_back(u);
	}
	void reset() {
		for(int i = 0; i < n; i++) {
			for(int j = 0; j < n; j++) {
				cap[i][j] = flow[i][j] = 0;
			}
			g[i].clear();
		}
	}
	inline Capacity residue(int u, int v) { return cap[u][v] - flow[u][v]; }
	Capacity solve(int s_, int t_) {
		this->t = t_, this->s = s_;
		que.resize(n + 1);
		Capacity res = 0;
		while(levelize()) { prog.assign(n, 0); res += augment(s, inf); }
		return res;
	}
	bool levelize() {
		int l = 0, r = 0;
		level.assign(n, -1); level[s] = 0; que[r++] = s;
		while(l != r) {
			int v = que[l++]; if(v == t) break;
			for(int i = 0; i < g[v].size(); i++) {
				const int& d = g[v][i];
				if(level[d] == -1 && residue(v, d) != 0) {
					level[d] = level[v] + 1; que[r++] = d;
				}
			}
		}
		return level[t] != -1;
	}
	Capacity augment(int v, Capacity lim) {
		Capacity res = 0;
		if(v == t) return lim;
		for(int &i = prog[v]; i < (int)g[v].size(); i++) {
			const int &d = g[v][i];
			if(residue(v, d) == 0 || level[v] >= level[d]) continue;
			const Capacity aug = augment(d, min(lim, residue(v, d)));
			flow[v][d] += aug; flow[d][v] -= aug;
			res += aug; lim -= aug;
			if(lim == 0) break;
		}
		return res;
	}
};


int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);

	int N, M;
	cin >> N;

	Dinic dinic(2 * N + 2);
	int S = 2 * N, T = S + 1;

	int sum = 0;
	for(int i = 0; i < N; i++) {
		int b, c;
		cin >> b >> c;
		dinic.add_edge(S, i, b);
		dinic.add_edge(i, N + i, 10000000);
		dinic.add_edge(N + i, T, c);
		sum += b + c;
	}

	cin >> M;
	for(int i = 0; i < M; i++) {
		int d, e;
		cin >> d >> e;
		dinic.add_edge(N + d, e, 10000000);
	}

	cout << sum - dinic.solve(S, T) << endl;
}