using System;
using System.Linq;
using System.Collections.Generic;
using Debug = System.Diagnostics.Debug;
using StringBuilder = System.Text.StringBuilder;
using System.Numerics;
namespace Program
{

    public class Solver
    {
        public void Solve()
        {
            var n = sc.Integer();
            var G = Enumerate(202, x => new List<Edge<int>>());
            var sum = 0;
            for (int i = 0; i < n; i++)
            {
                var b = sc.Integer();
                var c = sc.Integer();
                sum += b + c;
                G.AddDirectedEdge(200, i, b);
                G.AddDirectedEdge(i + 100, 201, c);
                G.AddDirectedEdge(i, i + 100, 100000);
            }
            var m = sc.Integer();
            for (int i = 0; i < m; i++)
            {
                var d = sc.Integer();
                var e = sc.Integer();
                G.AddDirectedEdge(d, e + 100, 100000);
            }
            var mincost = Flow.GetMaxFlow(G, 200, 201);
            IO.Printer.Out.WriteLine(sum - mincost);

        }
        public IO.StreamScanner sc = new IO.StreamScanner(Console.OpenStandardInput());
        static T[] Enumerate<T>(int n, Func<int, T> f) { var a = new T[n]; for (int i = 0; i < n; ++i) a[i] = f(i); return a; }
        static public void Swap<T>(ref T a, ref T b) { var tmp = a; a = b; b = tmp; }
    }
}

#region Ex
namespace Program.IO
{
    using System.IO;
    using System.Text;
    using System.Globalization;
    public class Printer : StreamWriter
    {
        static Printer() { Out = new Printer(Console.OpenStandardOutput()) { AutoFlush = false }; }
        public static Printer Out { get; set; }
        public override IFormatProvider FormatProvider { get { return CultureInfo.InvariantCulture; } }
        public Printer(System.IO.Stream stream) : base(stream, new UTF8Encoding(false, true)) { }
        public Printer(System.IO.Stream stream, Encoding encoding) : base(stream, encoding) { }
        public void Write<T>(string format, IEnumerable<T> source) { base.Write(format, source.OfType<object>().ToArray()); }
        public void WriteLine<T>(string format, IEnumerable<T> source) { base.WriteLine(format, source.OfType<object>().ToArray()); }
    }
    public class StreamScanner
    {
        public StreamScanner(Stream stream) { str = stream; }
        public readonly Stream str;
        private readonly byte[] buf = new byte[1024];
        private int len, ptr;
        public bool isEof = false;
        public bool IsEndOfStream { get { return isEof; } }
        private byte read()
        {
            if (isEof) return 0;
            if (ptr >= len) { ptr = 0; if ((len = str.Read(buf, 0, 1024)) <= 0) { isEof = true; return 0; } }
            return buf[ptr++];
        }
        public char Char() { byte b = 0; do b = read(); while ((b < 33 || 126 < b) && !isEof); return (char)b; }

        public string Scan()
        {
            var sb = new StringBuilder();
            for (var b = Char(); b >= 33 && b <= 126; b = (char)read())
                sb.Append(b);
            return sb.ToString();
        }
        public long Long()
        {
            if (isEof) return long.MinValue;
            long ret = 0; byte b = 0; var ng = false;
            do b = read();
            while (b != '-' && (b < '0' || '9' < b));
            if (b == '-') { ng = true; b = read(); }
            for (; true; b = read())
            {
                if (b < '0' || '9' < b)
                    return ng ? -ret : ret;
                else ret = ret * 10 + b - '0';
            }
        }
        public int Integer() { return (isEof) ? int.MinValue : (int)Long(); }
        public double Double() { return double.Parse(Scan(), CultureInfo.InvariantCulture); }
        private T[] enumerate<T>(int n, Func<T> f)
        {
            var a = new T[n];
            for (int i = 0; i < n; ++i) a[i] = f();
            return a;
        }

        public char[] Char(int n) { return enumerate(n, Char); }
        public string[] Scan(int n) { return enumerate(n, Scan); }
        public double[] Double(int n) { return enumerate(n, Double); }
        public int[] Integer(int n) { return enumerate(n, Integer); }
        public long[] Long(int n) { return enumerate(n, Long); }
    }
}

static class Ex
{
    static public string AsString(this IEnumerable<char> ie) { return new string(System.Linq.Enumerable.ToArray(ie)); }
    static public string AsJoinedString<T>(this IEnumerable<T> ie, string st = " ") { return string.Join(st, ie); }
    static public void Main()
    {
        var solver = new Program.Solver();
        solver.Solve();
        Program.IO.Printer.Out.Flush();
    }
}
#endregion
#region Edge
public class Edge<T>
{
    public int to, rev;
    public T cap;
    public Edge(int t, int r, T _cap) { to = t; rev = r; cap = _cap; }
    public override string ToString() { return string.Format("{0}: Capacity {1}", to, cap); }
}
#endregion
#region AddEdge
static public partial class Flow
{
    static public void AddDirectedEdge(this List<Edge<int>>[] G, int from, int to, int cap)
    {
        G[from].Add(new Edge<int>(to, G[to].Count, cap));
        G[to].Add(new Edge<int>(from, G[from].Count - 1, 0));
    }
    static public void AddUndirectedEdge(this List<Edge<int>>[] G, int from, int to, int cap)
    {
        G[from].Add(new Edge<int>(to, G[to].Count, cap));
        G[to].Add(new Edge<int>(from, G[from].Count - 1, cap));
    }
    static public void AddDirectedEdge(this List<Edge<long>>[] G, int from, int to, long cap)
    {
        G[from].Add(new Edge<long>(to, G[to].Count, cap));
        G[to].Add(new Edge<long>(from, G[from].Count - 1, 0));
    }
    static public void AddUndirectedEdge(this List<Edge<long>>[] G, int from, int to, long cap)
    {
        G[from].Add(new Edge<long>(to, G[to].Count, cap));
        G[to].Add(new Edge<long>(from, G[from].Count - 1, cap));
    }
}
#endregion

//MaxFlow   
#region Dinic
static public partial class Flow
{
    static public int GetMaxFlow(List<Edge<int>>[] G, int s, int t, int INF = 1<<30)
    {
        var n = G.Length;
        var level = new int[n];
        var iter = new int[n];


        Action<int> bfs = p =>
        {
            for (int i = 0; i < n; i++)
                level[i] = -1;
            var q = new Queue<int>();
            level[s] = 0;
            q.Enqueue(s);
            while (q.Any())
            {
                var v = q.Dequeue();
                foreach (var e in G[v])
                    if (e.cap > 0 && level[e.to] < 0)
                    {
                        level[e.to] = level[v] + 1;
                        q.Enqueue(e.to);
                    }
            }
        };


        Func<int, int, int, int> dfs = null;
        dfs = (v, u, f) =>
        {
            if (v == t) return f;
            for (; iter[v] < G[v].Count; iter[v]++)
            {
                var e = G[v][iter[v]];
                if (e.cap <= 0 || level[v] >= level[e.to]) continue;
                var d = dfs(e.to, u, Math.Min(f, e.cap));
                if (d <= 0) continue;
                e.cap -= d;
                G[e.to][e.rev].cap += d;
                return d;
            }
            return 0;
        };


        var flow = 0;
        while (true)
        {
            bfs(s);
            if (level[t] < 0) return flow;
            Array.Clear(iter, 0, iter.Length);
            int f;
            while ((f = dfs(s, t, INF)) > 0) flow += f;
        }
    }
}
#endregion