using System;
using System.Linq;
using System.Collections.Generic;
using Debug = System.Diagnostics.Trace;
using SB = System.Text.StringBuilder;
using Number = System.Int64;
using C = System.Int32;
using V = System.Int32;
namespace Program
{
    public class Solver
    {
        public void Solve()
        {
            var n = ri;
            var a = new int[n];
            var b = new int[n];
            for (int i = 0; i < n; i++)
            {
                a[i] = ri;
                b[i] = ri;
            }
            var xs = a.Concat(b).Distinct().ToList(); xs.Sort();
            var N = xs.Count;
            var G = new MinCostFlow(n + N + 2);
            var src = n + N;
            var sink = src + 1;
            for (int i = 0; i < n; i++)
            {
                G.AddDirectedEdge(src, i, 1, 0);
                var p = xs.BinarySearch(a[i]);
                var q = xs.BinarySearch(b[i]);
                G.AddDirectedEdge(i, n + p, 1, -xs[q]);
                G.AddDirectedEdge(i, n + q, 1, -xs[p]);
            }
            for (int i = 0; i < N; i++)
                G.AddDirectedEdge(n + i, sink, 1, 0);
            var fv = G.Execute(src, sink);
            Debug.WriteLine(fv);
            Console.WriteLine(-fv.Value);
        }
        const long INF = 1L << 60;
        //int[] dx = { -1, 0, 1, 0 };
        //int[] dy = { 0, 1, 0, -1 };
        //*
        int ri { get { return sc.Integer(); } }
        long rl { get { return sc.Long(); } }
        double rd { get { return sc.Double(); } }
        string rs { get { return sc.Scan(); } }
        //*/

        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 main
static class Ex
{
    static public string AsString(this IEnumerable<char> ie) { return new string(ie.ToArray()); }
    static public string AsJoinedString<T>(this IEnumerable<T> ie, string st = " ")
    {
        return string.Join(st, ie.Select(x => x.ToString()).ToArray());
        //return string.Join(st, ie);
    }
    static public void Main()
    {
        Console.SetOut(new System.IO.StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false });
        var solver = new Program.Solver();
        solver.Solve();
        Console.Out.Flush();
    }
}
#endregion
#region Ex
namespace Program.IO
{
    using System.IO;
    using System.Text;
    using System.Globalization;
    public class Printer: StreamWriter
    {
        public override IFormatProvider FormatProvider { get { return CultureInfo.InvariantCulture; } }
        public Printer(Stream stream) : base(stream, new UTF8Encoding(false, true)) { }
    }
    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 string ScanLine()
        {
            var sb = new StringBuilder();
            for (var b = Char(); b != '\n' && b != 0; b = (char)read())
                if (b != '\r') sb.Append(b);
            return sb.ToString();
        }
        public long Long() { return isEof ? long.MinValue : long.Parse(Scan()); }
        public int Integer() { return isEof ? int.MinValue : int.Parse(Scan()); }
        public double Double() { return isEof ? double.NaN : double.Parse(Scan(), CultureInfo.InvariantCulture); }
    }
}
#endregion



/// <summary>
/// ????????????????????????????°??????¨???????±????????????¨??????????????°????????§??????
/// </summary>
public class MinCostFlow
{
    bool hasng;
    readonly List<Edge>[] G;
    /// <summary>
    /// ????????° <paramref name="V"/> ??§???????????¨???????????°??????????§????????????????
    /// </summary>
    /// <param name="V">???????????°</param>
    /// <remarks>??????????????? O(<paramref name="V"/>) ??§?????????????????????</remarks>
    public MinCostFlow(int V)
    {
        G = new List<Edge>[V];
        for (int i = 0; i < V; i++)
            G[i] = new List<Edge>();

    }
    /// <summary>
    /// ?????? <paramref name="from"/> ???????????? <paramref name="to"/> ???????????? <paramref name="cap"/> ???????????? <paramref name="cost"/> ?????????????????????????????????
    /// </summary>
    /// <param name="from">?§??????¨??????????????? 0-indexed ??§?????????</param>
    /// <param name="to">????????¨??????????????? 0-indexed ??§?????????</param>
    /// <param name="cap">????????????</param>
    /// <param name="cost">???????????????</param>
    /// <remarks>??????????????? O(1) ??§?????????????????????</remarks>
    public void AddDirectedEdge(int from, int to, C cap, V cost)
    {
        addEdge(from, to, cap, 0, cost);
    }

    /// <summary>
    /// ?????? <paramref name="src"/> ???????????? <paramref name="sink"/> ????????§??§?????? <paramref name="f"/> ??????????°??????¨???????????????????????????
    /// </summary>
    /// <param name="src">???????????¨??????????????? 0-indexed ??§?????????</param>
    /// <param name="sink">???????????¨??????????????? 0-indexed ??§?????????</param>
    /// <param name="f">?????????????????????????????¨???????????§????????????-1?????????????????´??????????°??????¨?????§???????±??????????</param>
    /// <param name="inf">?????????????????????????????§????????¢????????§???</param>
    /// <remarks>???????????????Primal Dual???????????\?????????????¨??????? O(VE + FE log V) ??§?????????????????????V??????????????°???E???????????°???F??????????????¨????????????</remarks>
    public KeyValuePair<C, V> Execute(int src, int sink, C f = C.MaxValue, V inf = V.MaxValue / 3)
    {
        var n = G.Length;
        var dist = new V[n];
        var prev = new int[n];
        var prevEdge = new Edge[n];
        var potential = new V[n];


        C flow = 0;
        V cost = 0;
        var first = hasng;
        while (f > 0)
        {
            for (int i = 0; i < G.Length; i++)
                dist[i] = inf;

            //shortest path
            if (first)//spfa
            {
                var q = new Queue<int>();
                q.Enqueue(src); dist[src] = 0;
                var inQ = new bool[n];
                while (q.Count > 0)
                {
                    var p = q.Dequeue();
                    inQ[p] = false;
                    foreach (var e in G[p])
                    {
                        var t = e.To;
                        var d = dist[p] + e.Cost;
                        if (e.Cap > 0 && d < dist[t])
                        {
                            if (!inQ[t])
                            {
                                inQ[t] = true;
                                q.Enqueue(t);
                            }
                            dist[t] = d; prev[t] = p; prevEdge[t] = e;
                        }
                    }
                }
                first = false;
            }
            else//dijkstra
            {
                var vis = new bool[n];
                var pq = new PriorityQueue<KeyValuePair<int, V>>((l, r) => l.Value.CompareTo(r.Value));
                pq.Enqueue(new KeyValuePair<int, V>(src, 0));
                dist[src] = 0;
                while (pq.Count > 0)
                {
                    var p = pq.Dequeue().Key;
                    if (vis[p]) continue;
                    vis[p] = true;
                    foreach (var e in G[p])
                    {
                        if (e.Cap <= 0) continue;
                        var t = e.To;
                        if (vis[t]) continue;
                        var d = dist[p] + e.Cost + potential[p] - potential[t];
                        if (dist[t] > d)
                        {
                            dist[t] = d; prev[t] = p; prevEdge[t] = e;
                            pq.Enqueue(new KeyValuePair<int, V>(t, d));
                        }
                    }
                }


            }


            //update
            {
                if (dist[sink] == inf) break;
                for (int i = 0; i < n; i++)
                    potential[i] = Math.Min(inf, potential[i] + dist[i]);
                C df = f;
                V d = 0;
                for (var v = sink; v != src; v = prev[v])
                {
                    var e = prevEdge[v];
                    df = Math.Min(df, e.Cap); d += e.Cost;
                }
                if (d > 0) break;
                f -= df; cost += df * d; flow += df;
                for (var v = sink; v != src; v = prev[v])
                {
                    var e = prevEdge[v];
                    e.Cap -= df; e.Rev.Cap += df;
                }
            }

        }
        return new KeyValuePair<C, V>(flow, cost);
    }
    void addEdge(int f, int t, C c1, C c2, V e)
    {
        if (e < 0) hasng = true;
        var a = new Edge(t, c1, e);
        var b = new Edge(f, c2, -e);
        Edge.Link(a, b);
        G[f].Add(a);
        G[t].Add(b);
    }
    class Edge
    {
        public static void Link(Edge e1, Edge e2)
        {
            e1.Rev = e2; e2.Rev = e1;
        }
        public int To { get; private set; }
        public Edge Rev { get; private set; }
        public V Cost { get; private set; }
        public C Cap { get; set; }
        public Edge(int t, C c, V e)
        {
            To = t;
            Cap = c;
            Cost = e;
        }
        public override string ToString()
        {
            return string.Format("to: {0}, cap: {1}", To, Cap);
        }
    }
}
#region BinaryHeap
public class PriorityQueue<T>
{
    readonly List<T> heap = new List<T>();
    readonly Comparison<T> compare;
    public PriorityQueue() { compare = Comparer<T>.Default.Compare; }

    public PriorityQueue(Comparison<T> comparison) { compare = comparison; }
    public PriorityQueue(IComparer<T> comparer) { compare = comparer.Compare; }

    public void Enqueue(T item)
    {
        var pos = heap.Count;
        heap.Add(item);
        while (pos > 0)
        {
            var par = (pos - 1) / 2;
            if (compare(heap[par], item) <= 0)
                break;
            heap[pos] = heap[par];
            pos = par;
        }
        heap[pos] = item;

    }

    public T Dequeue()
    {
        var ret = heap[0];
        var pos = 0;
        var x = heap[heap.Count - 1];

        while (pos * 2 + 1 < heap.Count - 1)
        {
            var lch = pos * 2 + 1;
            var rch = pos * 2 + 2;
            if (rch < heap.Count - 1 && compare(heap[rch], heap[lch]) < 0) lch = rch;
            if (compare(heap[lch], x) >= 0)
                break;
            heap[pos] = heap[lch];
            pos = lch;
        }
        heap[pos] = x;
        heap.RemoveAt(heap.Count - 1);
        return ret;

    }
    public T Peek() { return heap[0]; }
    public int Count { get { return heap.Count; } }
    public bool Any() { return heap.Count > 0; }

    public T[] Items
    {
        get
        {
            var ret = heap.ToArray();
            Array.Sort(ret, compare);
            return ret;
        }
    }
}
#endregion


Measured memory_bytes: 13072