#include <bits/stdc++.h>
#define GET_MACRO(a, b, c, NAME, ...) NAME
#define rep(...) GET_MACRO(__VA_ARGS__, rep3, rep2)(__VA_ARGS__)
#define rep2(i, a) rep3 (i, 0, a)
#define rep3(i, a, b) for (int i = (a); i < (b); i++)
#define repr(...) GET_MACRO(__VA_ARGS__, repr3, repr2)(__VA_ARGS__)
#define repr2(i, a) repr3 (i, 0, a)
#define repr3(i, a, b) for (int i = (b) - 1; i >= (a); i--)
#define chmin(a, b) ((b) < a && (a = (b), true))
#define chmax(a, b) (a < (b) && (a = (b), true))
using namespace std;
typedef long long ll;

class MaxFlow {
public:
	MaxFlow(int V) : G(V), level(V), iter(V) {}
	void add(int u, int v, int cap) {
		G[u].push_back((edge){v, cap, (int)G[v].size()});
		G[v].push_back((edge){u, 0, (int)G[u].size() - 1});
	}
	int calc(int s, int t) {
		int res = 0;
		for (;;) {
			bfs(s);
			if (level[t] < 0) return res;
			fill(iter.begin(), iter.end(), 0);
			int f;
			while ((f = dfs(s, t, (int)1e9)) > 0) {
				res += f;
			}
		}
	}
private: 
	struct edge { int to, cap, rev; };
	vector<int> level, iter;
	vector<vector<edge> > G;
	void bfs(int s) {
		fill(level.begin(), level.end(), -1);
		queue<int> q;
		q.push(s);
		level[s] = 0;
		while (!q.empty()) {
			int v = q.front(); q.pop();
			for (edge e : G[v]) {
				if (e.cap > 0 && level[e.to] < 0) {
					level[e.to] = level[v] + 1;
					q.push(e.to);
				}
			}
		}
	}
	int dfs(int v, int t, int f) {
		if (v == t) return f;
		for (int &i = iter[v]; i < G[v].size(); i++) {
			edge &e = G[v][i];
			if (e.cap > 0 && level[v] < level[e.to]) {
				int d = dfs(e.to, t, min(f, e.cap));
				if (d > 0) {
					e.cap -= d;
					G[e.to][e.rev].cap += d;
					return d;
				}
			}
		}
		return 0;
	}
};

int main() {
	int N;
	cin >> N;
	MaxFlow f(N * 2 + 2);
	const int inf = 1e7;
	int s = N * 2;
	int t = N * 2 + 1;
	int ans = 0;
	rep (i, N) {
		int B, C;
		cin >> B >> C;
		int mx = max(B, C);
		ans += mx;
		f.add(s, i, mx - B);
		f.add(i, i + N, mx);
		f.add(i + N, t, mx - C);
	}
	int M;
	cin >> M;
	rep (i, M) {
		int D, E;
		cin >> D >> E;
		f.add(E + N, D, inf);
	}
	ans -= f.calc(s, t);
	cout << ans << endl;
	return 0;
}