#include <map>
#include <cstdio>
#include <algorithm>
#include <queue>
#define REP(i,n) for(int i=0; i<(int)(n); i++)

inline int getInt(){ int s; scanf("%d", &s); return s; }

using namespace std;

template<class T>
class IdMaker{
public:
  std::map<T,int> _m;
  int getId(const T &v){
    if(_m.find(v) == _m.end()){
      int next = _m.size();
      return _m[v] = next;
    }
    return _m[v];
  }
};

struct Edge{
  int cap; // capacity
  int to;
  int rev; // reverse edge id

  Edge(){}
  Edge(int c, int t, int r) :
    cap(c), to(t), rev(r){}
};

struct CostEdge : public Edge{
  int cost;
  CostEdge() : Edge() {}
  CostEdge(int c, int t, int cs, int r) :
    Edge(c, t, r), cost(cs){}
};

template<class E> // Edge type
class Graph{
public:
  typedef std::vector<std::vector<E> > G;

private:
  G g;

public:
  Graph(int n) : g(G(n)) {}

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

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

  G &getRowGraph(){
    return g;
  }
};

template<class E>
int minCostFlow(Graph<E> &graph, int s, int t, int f, bool negative = false){
  typedef pair<int, int> P;
  typename Graph<E>::G &g = graph.getRowGraph();
  int n = g.size();
  int res = 0;
  vector<int> h(n, 0);
  vector<int> prevv(n);
  vector<int> preve(n);
  const int inf = 10000000;

  if(negative){
    vector<int> dist(n, inf);
    dist[s] = 0;

    bool update = true;

    while(update){
      update = false;
      for(int v = 0; v < n; v++){
        if(dist[v] == inf) continue;
        for(int i = 0; i < (int)g[v].size(); i++){
          E &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;
          }
        }
      }
    }

    for(int i = 0; i < n; i++)
      h[i] = dist[i];
  }

  while(f > 0){
    priority_queue<P, vector<P>, greater<P> > que;
    vector<int> dist(n, inf);
    dist[s] = 0;
    que.push(P(0, s));

    while(!que.empty()){
      P p   = que.top(); que.pop();
      int v = p.second;
      if(dist[v] < p.first) continue;
      for(int i = 0; i < (int)g[v].size(); i++){
        E &e = g[v][i];

        if(e.cap > 0 && dist[e.to] > dist[v] + e.cost + h[v] - h[e.to]){
          dist[e.to]  = dist[v] + e.cost + h[v] - h[e.to];
          prevv[e.to] = v;
          preve[e.to] = i;
          que.push(P(dist[e.to], e.to));
        }
      }
    }

    if(dist[t] == inf){
      return -1;
    }

    for(int v = 0; v < n; v++) h[v] += dist[v];

    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 * h[t];

    for(int v = t; v != s; v = prevv[v]){
      E &e = g[prevv[v]][preve[v]];
      e.cap -= d;
      g[v][e.rev].cap += d;
    }
  }
  return res;
}

int main(){
  IdMaker<int> idm;
  const int n = getInt();
  vector<int> a(n);
  vector<int> b(n);

  REP(i,n){
    a[i] = getInt();
    b[i] = getInt();

    idm.getId(a[i]);
    idm.getId(b[i]);
  }

  const int m = n + idm._m.size() + 3;
  const int s = n + idm._m.size();
  const int d = s + 1;
  const int dammy = d + 1;

  Graph<CostEdge> g(m);

  REP(i,n){
    g.addEdge(s, i, 1, 0);
    g.addEdge(i, n + idm.getId(a[i]), 1, -b[i]);
    g.addEdge(i, n + idm.getId(b[i]), 1, -a[i]);
  }

  REP(i, idm._m.size()){
    g.addEdge(n + i, d, 1, 0);
  }

  g.addEdge(s, dammy, 1000000, 0);
  g.addEdge(dammy, d, 1000000, 0);

  const int ans = - minCostFlow(g, s, d, n, true);

  printf("%d\n", ans);

  return 0;
}

Measured memory_bytes: 1188