#include "bits/stdc++.h"
using namespace std;
#define FOR(i,j,k) for(int (i)=(j);(i)<(int)(k);++(i))
#define rep(i,j) FOR(i,0,j)
#define each(x,y) for(auto &(x):(y))
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define debug(x) cout<<#x<<": "<<(x)<<endl
#define smax(x,y) (x)=max((x),(y))
#define smin(x,y) (x)=min((x),(y))
#define MEM(x,y) memset((x),(y),sizeof (x))
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<ll> vll;

struct FordFulkerson{
    struct E{ int to, cap, rev; };
    vector<vector<E>> G;
    vector<bool> used;
    FordFulkerson(int n) : G(n), used(n){
    }

    void add_edge(int from, int to, int cap){
        G[from].push_back(E{ to, cap, (int)G[to].size() });
        G[to].push_back(E{ from, 0, (int)G[from].size() - 1 });
    }

    int dfs(int v, int t, int f){
        if (v == t) return f;
        used[v] = 1;
        for (auto &e : G[v]){
            if (!used[e.to] && e.cap > 0){
                int d = dfs(e.to, t, min(e.cap, f));
                if (d > 0){
                    e.cap -= d;
                    G[e.to][e.rev].cap += d;
                    return d;
                }
            }
        }
        return 0;
    }

    int maxflow(int s, int t){
        int f = 1, res = 0;
        while (f){
            fill(begin(used), end(used), false);
            f = dfs(s, t, 1 << 30);
            res += f;
        }
        return res;
    }
};

int main(){
    int N, S, T, INF = 10000, s = 0;
    cin >> N;
    S = 2 * N, T = 2 * N + 1;
    FordFulkerson ff(2 * N + 2);
    rep(i, N){
        int B, C;
        cin >> B >> C;
        ff.add_edge(S, i, B);
        ff.add_edge(i, N + i, INF);
        ff.add_edge(N + i, T, C);
        s += B + C;
    }
    int M; cin >> M;
    rep(i, M){
        int D, E;
        cin >> D >> E;
        ff.add_edge(D, N + E, INF);
    }
    int ans = s - ff.maxflow(S, T);
    cout << ans << endl;
}