#include <iostream>
#include <sstream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <ctime>
#include <cstring>
#include <string>
#include <vector>
#include <stack>
#include <queue>
#include <deque>
#include <map>
#include <set>
#include <bitset>
#include <numeric>
#include <utility>
#include <iomanip>
#include <algorithm>
#include <functional>
using namespace std;

typedef long long ll;
typedef vector<int> vint;
typedef vector<ll> vll;
typedef pair<int,int> pint;

#define DE 1
#define FI first
#define SE second
#define PB push_back
#define MP make_pair
#define ALL(s) (s).begin(),(s).end()
#define REP(i,n) for (int i = 0; i < (int)(n); ++i)
#define EACH(i,s) for (__typeof__((s).begin()) i = (s).begin(); i != (s).end(); ++i)
#define COUT(x) cout<<#x<<" = "<<(x)<<" (L"<<__LINE__<<")"<<endl

template<class T1, class T2> ostream& operator<<(ostream &s, pair<T1,T2> P){return s<<'<'<<P.first<<", "<<P.second<<'>';}
template<class T> ostream& operator<<(ostream &s, vector<T> P) {s<<"{ ";for(int i=0;i<P.size();++i){if(i>0)s<<", ";s<<P[i];}return s<<" }"<<endl;}
template<class T1, class T2> ostream& operator<<(ostream &s, map<T1,T2> P) {s<<"{ ";for(__typeof__(P.begin()) it=P.begin();it!=P.end();++it){if(it!=P.begin())s<<", ";s<<'<'<<it->first<<"->"<<it->second<<'>';}return s<<" }"<<endl;}



struct Edge {
    int rev, from, to, cap, icap, flow, cost;
    Edge() {}
    Edge(int r, int f, int t, int ca, int co) : rev(r), from(f), to(t), cap(ca), icap(ca), flow(0), cost(co) {}
    friend bool operator < (const Edge &e1, const Edge &e2) {return e1.cost < e2.cost;}
    friend ostream& operator << (ostream& s, const Edge& E) {s << E.from << "->" << E.to << '(' << E.cap << ',' << E.cost << ')';return s;}
};

const int MAX_V = 5000;
struct Graph {
    int V,E;
    vector<Edge> list[MAX_V];
    
    Graph(int n = 0) : V(n), E(0) {}
    void init(int n = 0) {V = n; E = 0; for (int i = 0; i < MAX_V; ++i) list[i].clear();}
	void resize(int n = 0) {V = n;}
    void reset() {for (int i = 0; i < V; ++i) for (int j = 0; j < list[i].size(); ++j) list[i][j].cap = list[i][j].icap;}
    inline vector<Edge>& operator [] (int i) {return list[i];}
    friend ostream& operator << (ostream& s, const Graph& G) {for (int i = 0; i < G.V; ++i) {s << i << " : " << G.list[i];}return s;}
    
    void addedge(int from, int to, int cap, int cost) {
        if (cap > 0) {
            ++E;
            list[from].push_back(Edge(list[to].size(), from, to, cap, cost));
            list[to].push_back(Edge(list[from].size()-1, to, from, 0, -cost));
        }
    }
    
    Edge &redge(Edge e) {
        if (e.from != e.to) return list[e.to][e.rev];
        else return list[e.to][e.rev+1];
    }
};

Graph G;

int dist[MAX_V];
int prevv[MAX_V];
int preve[MAX_V];

const ll INF = 1LL<<30;
int MinCost(Graph &G, int s, int t, int f) {
    int res = 0;
    while (f > 0) {
        fill(dist, dist+G.V, INF);
        dist[s] = 0;
        while (true) {
            bool update = false;
            for (int v = 0; v < G.V; ++v) {
                if (dist[v] == INF) continue;
                for (int i = 0; i < G[v].size(); ++i) {
                    Edge &e = G[v][i];
                    if (e.cap > 0 && dist[e.to] > dist[v] + e.cost) {
                        dist[e.to] = dist[v] + e.cost;
                        prevv[e.to] = v;
                        preve[e.to] = i;
                        update = true;
                    }
                }
            }
            if (!update) break;
        }
        
        if (dist[t] == INF) return -1;
        
        int d = f;
        for (int v = t; v != s; v = prevv[v]) {
            d = min(d, G[prevv[v]][preve[v]].cap);
        }
        f -= d;
        res += d * dist[t];
        for (int v = t; v != s; v = prevv[v]) {
            Edge &e = G[prevv[v]][preve[v]];
            Edge &re = G.redge(e);
            e.cap -= d;
            re.cap += d;
        }
    }
    return res;
}

int n;
int a, b;
vector<pint> block;
map<int,int> ind;

int main() {
    //freopen( "/Users/macuser/Documents/Programming/Contest/input.in", "r", stdin );
    
    while (cin >> n) {
        block.clear(); ind.clear();
        int id = 0;
        for (int i = 0; i < n; ++i) {
            cin >> a >> b;
            block.PB(MP(a,b));
            if (!ind.count(a)) {ind[a] = id; ++id;}
            if (!ind.count(b)) {ind[b] = id; ++id;}
        }
        int V = n + id + 2;
        int s = V-2, t = V-1;
        G.init(V);
        
        G.addedge(s, t, 1000000, 0);
        for (int i = 0; i < n; ++i) G.addedge(s, i, 1, 0);
        for (int i = 0; i < id; ++i) G.addedge(i+n, t, 1, 0);
        for (int i = 0; i < n; ++i) {
            int from = i;
            int to1 = ind[block[i].FI], to2 = ind[block[i].SE];
            G.addedge(from, to1+n, 1, -block[i].SE);
            if (to2 != to1) G.addedge(from, to2+n, 1, -block[i].FI);
        }
        //COUT(G);
        
        int res = MinCost(G, s, t, n);
        
        //COUT(G);
        
        cout << -res << endl;
    }
    
    return 0;
}


Measured memory_bytes: 1800