#include <string>
#include <vector>
#include <algorithm>
#include <numeric>
#include <set>
#include <map>
#include <queue>
#include <iostream>
#include <sstream>
#include <cstdio>
#include <cmath>
#include <ctime>
#include <cstring>
#include <cctype>
#include <cassert>
#include <limits>
#include <functional>
#define rep(i,n) for(int (i)=0;(i)<(int)(n);++(i))
#define rer(i,l,u) for(int (i)=(int)(l);(i)<=(int)(u);++(i))
#define reu(i,l,u) for(int (i)=(int)(l);(i)<(int)(u);++(i))
#if defined(_MSC_VER) || __cplusplus > 199711L
#define aut(r,v) auto r = (v)
#else
#define aut(r,v) __typeof(v) r = (v)
#endif
#define each(it,o) for(aut(it, (o).begin()); it != (o).end(); ++ it)
#define all(o) (o).begin(), (o).end()
#define pb(x) push_back(x)
#define mp(x,y) make_pair((x),(y))
#define mset(m,v) memset(m,v,sizeof(m))
#define INF 0x3f3f3f3f
#define INFL 0x3f3f3f3f3f3f3f3fLL
using namespace std;
typedef vector<int> vi; typedef pair<int,int> pii; typedef vector<pair<int,int> > vpii; typedef long long ll;
template<typename T, typename U> inline void amin(T &x, U y) { if(y < x) x = y; }
template<typename T, typename U> inline void amax(T &x, U y) { if(x < y) x = y; }

struct MaximumFlow {
	typedef int Index;
	typedef int Flow;
	static const Flow InfCapacity = INF;
	struct Edge {
		Index to;
		Flow capacity;
		Index rev;
	};
	vector<vector<Edge> > g;
	void init(Index n) { g.assign(n, vector<Edge>()); }
	void add(Index i, Index j, Flow capacity) {
		Edge e, f; e.to = j, f.to = i; e.capacity = capacity, f.capacity = 0;
		g[i].push_back(e); g[j].push_back(f);
		g[i].back().rev = (Index)g[j].size() - 1; g[j].back().rev = (Index)g[i].size() - 1;
	}
	void addB(Index i, Index j, Flow capacity) {
		Edge e, f; e.to = j, f.to = i; e.capacity = capacity, f.capacity = capacity;
		g[i].push_back(e); g[j].push_back(f);
		g[i].back().rev = (Index)g[j].size() - 1; g[j].back().rev = (Index)g[i].size() - 1;
	}
	//gを破壊する
	Flow maximumFlow(int s, int t) {
		int n = g.size();
		vector<Index> level(n);
		Flow total = 0; bool update;
		do {
			update = false;
			fill(level.begin(), level.end(), -1); level[s] = 0;
			queue<Index> q; q.push(s);
			for(Index d = n; !q.empty() && level[q.front()] < d; ) {
				int u = q.front(); q.pop();
				if(u == t) d = level[u];
				each(e, g[u]) if(e->capacity > 0 && level[e->to] == -1)
					q.push(e->to), level[e->to] = level[u] + 1;
			}
			vector<Index> iter(n);
			for(Index i = 0; i < n; i ++) iter[i] = (int)g[i].size() - 1;
			while(1) {
				Flow f = augment(level, iter, s, t, InfCapacity);
				if(f == 0) break;
				total += f; update = true;
			}
		}while(update);
		return total;
	}
	Flow augment(vector<Index> &level, vector<Index> &iter, Index u, Index t, Flow f) {
		if(u == t || f == 0) return f;
		Index lv = level[u];
		if(lv == -1) return 0;
		level[u] = -1;
		for(; iter[u] >= 0; -- iter[u]) {
			Edge &e = g[u][iter[u]];
			if(level[e.to] <= lv) continue;
			Flow l = augment(level, iter, e.to, t, min(f, e.capacity));
			if(l == 0) continue;
			e.capacity -= l; g[e.to][e.rev].capacity += l;
			level[u] = lv;
			return l;
		}
		return 0;
	}
};

int main() {
	int N;
	while(~scanf("%d", &N)) {
		vector<int> B(N);
		vector<int> C(N);
		for(int i = 0; i < N; ++ i)
			scanf("%d%d", &B[i], &C[i]);
		int M;
		scanf("%d", &M);
		vector<int> D(M);
		vector<int> E(M);
		for(int i = 0; i < M; ++ i)
			scanf("%d%d", &D[i], &E[i]);
		MaximumFlow mf;
		int src = N * 2, dst = src + 1;
		mf.init(dst + 1);
		int sum = 0;
		rep(i, N) {
			//行かない: 0,1 あるいは  1,0
			//行って、参加する: 1,1
			//行って、参加しない: 0,0
			//"行かない"に対応する状態が2つあることがポイントか
			mf.add(src, i, B[i]);
			mf.add(i, N + i, B[i] + C[i]);
			mf.add(N + i, dst, C[i]);
			sum += B[i] + C[i];
		}
		rep(i, M)
			mf.add(N + D[i], E[i], INF);
		int f = mf.maximumFlow(src, dst);
		int ans = sum - f;
		printf("%d\n", ans);
	}
	return 0;
}