#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef pair<int, int> P;

#define For(i, a, b) for(int i = (a); i < (b); i++)
#define Rep(i, n) For(i, 0, (n))
#define Rrep(i, n) for(int i = (n - 1); i >= 0; i--)
#define Itr(i, c) for(typeof(c.begin()) i = c.begin(); i != c.end(); i++)
#define pb push_back

const int inf = 999999999;
const int mod = 1000000007;
const int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};

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

vector<edge> G[82];
bool used[82];

void add_edge(int from, int to, int cap){
	int p = G[to].size(), q = G[from].size();
	G[from].pb((edge){to, cap, p});
	G[to].pb((edge){from, 0, q});
}

int dfs(int v, int t, int f){
	if(v == t) return f;
	used[v] = true;
	for(int i = 0; i < G[v].size(); i++){
		edge &e = G[v][i];
		if(!used[e.to] && e.cap > 0){
			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 max_flow(int s, int t){
	int flow = 0;
	while(1){
		Rep(i, sizeof(used)/sizeof(*used)){
			used[i] = false;
		}
		int f = dfs(s, t, inf);
		if(f == 0) return flow;
		flow += f;
	}
}

int main(){
	int n, m, sum = 0; cin >> n;
	Rep(i, n){
		int b, c; cin >> b >> c;
		sum += max(b, c);
		add_edge(80, i * 2, max(b, c) - c);
		add_edge(i * 2 + 1, 81, max(b, c) - b);
		add_edge(i * 2, i * 2 + 1, max(b, c));
	}
	cin >> m;
	Rep(i, m){
		int d, e;
		cin >> d >> e;
		add_edge(d * 2 + 1, e * 2, inf);
	}
	int f = max_flow(80, 81);
	cout << sum - f << endl;
	return 0;
}