using System;
using System.IO;
using System.Linq;
using System.Text;
using System.Collections.Generic;
using System.Diagnostics;
using System.Numerics;
using Enu = System.Linq.Enumerable;

class Program
{
    public void Solve()
    {
        int N = Reader.Int();
        var Val = Reader.IntTable(N);
        int M = Reader.Int();
        var Es = Reader.IntTable(M);
        int S = N * 2, T = S + 1;
        var dinic = new Dinic(T + 1);

        for (int i = 0; i < N; i++)
        {
            dinic.AddEdge(S, i, Val[i][0]);
            dinic.AddEdge(i, N + i, Dinic.INF);
            dinic.AddEdge(N + i, T, Val[i][1]);
        }
        foreach (var e in Es)
            dinic.AddEdge(e[0], N + e[1], Dinic.INF);

        int ans = Val.Sum(v => v.Sum()) - dinic.MaxFlow(S, T);

        Console.WriteLine(ans);
    }

    class Dinic
    {
        public static readonly int INF = (int)1e9;
        List<Edge>[] G;
        int S, T;
        int[] level;
        int[] iter;

        public Dinic(int V)
        {
            G = new List<Edge>[V];
            for (int i = 0; i < V; i++) G[i] = new List<Edge>();
        }
        public void AddEdge(int from, int to, int capacity)
        {
            G[from].Add(new Edge(to, capacity, G[to].Count));
            G[to].Add(new Edge(from, 0, G[from].Count - 1));
        }
        public int MaxFlow(int s, int t)
        {
            S = s; T = t;
            int flow = 0;
            while (true)
            {
                BFS();
                if (level[T] < 0) return flow;
                iter = new int[G.Length];
                int f;
                while ((f = DFS(S, INF)) > 0) { flow += f; }
            }
        }
        private void BFS()
        {
            level = Enumerable.Repeat(-1, G.Length).ToArray();
            Queue<int> que = new Queue<int>();
            que.Enqueue(S);
            level[S] = 0;
            while (que.Count > 0)
            {
                int v = que.Dequeue();
                foreach (Edge e in G[v])
                    if (e.capacity > 0 && level[e.to] < 0)
                    {
                        level[e.to] = level[v] + 1;
                        que.Enqueue(e.to);
                    }
            }
        }
        private int DFS(int v, int flow)
        {
            if (v == T) return flow;
            while (iter[v] < G[v].Count)
            {
                Edge e = G[v][iter[v]];
                if (e.capacity > 0 && level[v] < level[e.to])
                {
                    int d = DFS(e.to, Math.Min(flow, e.capacity));
                    if (d > 0)
                    {
                        e.capacity -= d;
                        G[e.to][e.reverse].capacity += d;
                        return d;
                    }
                }
                iter[v]++;
            }
            return 0;
        }

        class Edge
        {
            public int to, reverse;
            public int capacity;
            public Edge(int to, int capacity, int reverse)
            {
                this.to = to;
                this.capacity = capacity;
                this.reverse = reverse;
            }
        }
    }
}


class Entry { static void Main() { new Program().Solve(); } }
class Reader
{
    private static TextReader reader = Console.In;
    private static readonly char[] separator = { ' ' };
    private static readonly StringSplitOptions op = StringSplitOptions.RemoveEmptyEntries;
    private static string[] A = new string[0];
    private static int i;
    private static void Init() { A = new string[0]; }
    public static void Set(TextReader r) { reader = r; Init(); }
    public static void Set(string file) { reader = new StreamReader(file); Init(); }
    public static bool HasNext() { return CheckNext(); }
    public static string String() { return Next(); }
    public static int Int() { return int.Parse(Next()); }
    public static long Long() { return long.Parse(Next()); }
    public static double Double() { return double.Parse(Next()); }
    public static int[] IntLine() { return Array.ConvertAll(Split(Line()), int.Parse); }
    public static int[] IntArray(int N) { return Enu.Range(0, N).Select(i => Int()).ToArray(); }
    public static int[][] IntTable(int H) { return Enu.Range(0, H).Select(i => IntLine()).ToArray(); }
    public static string[] StringArray(int N) { return Enu.Range(0, N).Select(i => Line()).ToArray(); }
    public static string Line() { return reader.ReadLine().Trim(); }
    private static string[] Split(string s) { return s.Split(separator, op); }
    private static string Next() { CheckNext(); return A[i++]; }
    private static bool CheckNext()
    {
        if (i < A.Length) return true;
        string line = reader.ReadLine();
        if (line == null) return false;
        if (line == "") return CheckNext();
        A = Split(line);
        i = 0;
        return true;
    }
}