#include <algorithm>
#include <iostream>
#include <cstdio>
#include <map>
#include <numeric>
#include <cmath>
#include <set>
#include <sstream>
#include <string>
#include <vector>
#include <queue>
#include <stack>
#include <complex>
#include <string.h>
#include <unordered_set>
#include <unordered_map>
#include <bitset>
#include <iomanip>
#include <sys/time.h>
#include <random>
using namespace std;

#define endl '\n'
#define ALL(v) (v).begin(), (v).end()
#define RALL(v) (v).rbegin(), (v).rend()
#define UNIQ(v) (v).erase(unique((v).begin(), (v).end()), (v).end())

typedef long long ll;
typedef long double ld;
typedef pair<int, int> P;
typedef complex<double> comp;
typedef vector< vector<ld> > matrix;
struct pairhash {
public:
    template<typename T, typename U>
    size_t operator()(const pair<T, U> &x) const {
	size_t seed = hash<T>()(x.first);
	return hash<U>()(x.second) + 0x9e3779b9 + (seed<<6) + (seed>>2);
    }
};
const int inf = 1e9 + 9;
const ll mod = 1e9 + 7;
const double eps = 1e-8;
const double pi = acos(-1);

const int MAX = 100;
struct edge {
    int to, cap, rev;
};

vector<edge> G[MAX];
int level[MAX];
int iter[MAX];

int n;
int b[50], c[50];
int m;
int d[50*50], e[50*50];

void add_edge(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});
}

void bfs(int s) {
    memset(level, -1, sizeof(level));
    queue<int> que;
    level[s] = 0;
    que.push(s);
    while (!que.empty()) {
        int v = que.front(); que.pop();
        for (int i = 0; i < G[v].size(); i++) {
            edge &e = G[v][i];
            if (e.cap > 0 and level[e.to] < 0) {
                level[e.to] = level[v] + 1;
                que.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 and 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 dinic(int s, int t) {
    int flow = 0;
    while (true) {
        bfs(s);
        if (level[t] < 0) return flow;
        memset(iter, 0, sizeof(iter));
        int f;
        while ((f = dfs(s, t, inf)) > 0) {
            flow += f;
        }
    }
}

int solve() {
    int sum = 0;
    int s = 2*n, t = 2*n+1;
    for (int i = 0; i < n; i++) {
        add_edge(s, 2*i, b[i]);
        add_edge(2*i, 2*i+1, inf);
        add_edge(2*i+1, t, c[i]);
        sum += b[i] + c[i];
    }
    for (int i = 0; i < m; i++) {
        add_edge(2*d[i], 2*e[i]+1, inf);
    }
    return sum - dinic(s, t);
}

void input() {
    cin >> n;
    for (int i = 0; i < n; i++) cin >> b[i] >> c[i];
    cin >> m;
    for (int i = 0; i < m; i++) cin >> d[i] >> e[i];
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << fixed << setprecision(15);

    input();
    cout << solve() << endl;
}