#include <iostream>
#include <vector>
#include <queue>
#define repeat(i,n) for (int i = 0; (i) < (n); ++(i))
typedef long long ll;
using namespace std;
ll maximum_flow(int s, int t, vector<vector<ll> > const & g /* capacity, adjacency matrix */) { // edmonds karp, O(E^2V)
    int n = g.size();
    vector<vector<ll> > flow(n, vector<ll>(n));
    auto residue = [&](int i, int j) { return g[i][j] - flow[i][j]; };
    ll result = 0;
    while (true) {
        vector<int> prev(n, -1);
        vector<ll> f(n);
        // find the shortest augmenting path
        queue<int> q; // bfs
        q.push(s);
        while (not q.empty()) {
            int i = q.front(); q.pop();
            repeat (j,n) if (prev[j] == -1 and j != s and residue(i,j) > 0) {
                prev[j] = i;
                f[j] = residue(i,j);
                if (i != s) f[j] = min(f[j], f[i]);
                q.push(j);
            }
        }
        if (prev[t] == -1) break; // not found
        // backtrack
        for (int i = t; prev[i] != -1; i = prev[i]) {
            int j = prev[i];
            flow[j][i] += f[t];
            flow[i][j] -= f[t];
        }
        result += f[t];
    }
    return result;
}
const ll INF = 1000000007;
int main() {
    int n; cin >> n;
    ll a = 0;
    vector<vector<ll> > g(2*n+2, vector<ll>(2*n+2));
    repeat (i,n) {
        ll b, c; cin >> b >> c;
        a += b + c;
        g[2*n][    i] = b;
        g[  i][  n+i] = INF;
        g[n+i][2*n+1] = c;
    }
    int m; cin >> m;
    repeat (i,m) {
        int d, e; cin >> d >> e;
        g[d][n+e] = INF;
    }
    cout << a - maximum_flow(2*n, 2*n+1, g) << endl;
    return 0;
}