#include <bits/stdc++.h>
using namespace std;
#define INF (2e9)
#define REP(i,n) for(int i=0;i<(int)n;++i)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();++i)
#define ALL(c) (c).begin(), (c).end()
typedef int Weight;
struct Edge {
  int src, dst;
  Weight weight;
  Weight capacity;
 
  Edge(int src, int dst, Weight weight) :
    src(src), dst(dst), weight(weight) { }
  Edge(int src, int dst, Weight capacity, Weight weight) : 
    src(src), dst(dst), capacity(capacity), weight(weight){ }
  Edge(int src, int dst) :
    src(src), dst(dst){weight=1;}
};
bool operator < (const Edge &e, const Edge &f) {
  return e.weight != f.weight ? e.weight > f.weight : // !!INVERSE!!
    e.src != f.src ? e.src < f.src : e.dst < f.dst;
}
typedef vector<Edge> Edges;
typedef vector<Edges> Graph;
typedef vector<Weight> Array;
typedef vector<Array> Matrix;

#define RESIDUE(u,v) (capacity[u][v] - flow[u][v])
#define RCOST(u,v) (cost[u][v] + h[u] - h[v])
pair<Weight, Weight> minimumCostFlow(Graph &g, int s, int t) {
  unordered_map<int,int> capacity[3333];
  unordered_map<int,int> cost[3333];
  unordered_map<int,int> flow[3333];
  
  const int n = g.size();
  REP(u,n) FOR(e,g[u]) {
    capacity[e->src][e->dst] += e->capacity;
    cost[e->src][e->dst] += e->weight;
  }
  pair<Weight, Weight> total; // (cost, flow)
  vector<Weight> h(n,INF);
  h[s] = 0;
  for(int k = 0 ; k <= g.size() ; k++){
	  int flag = 0;
	  for(int i = 0 ; i < g.size() ; i++){
		for( auto &e : g[i] ){
			if( e.capacity == 0 ) continue;
			if( h[e.dst] > h[e.src]+e.weight ){
				h[e.dst] = h[e.src]+e.weight;
				flag = 1;
			}
		}
	  }
	  if(!flag) break;
  }
  for (Weight F = INF; F > 0; ) { // residual flow
    vector<Weight> d(n, INF); d[s] = 0;
    vector<int> p(n, -1);
    priority_queue<Edge> Q; // "e < f" <=> "e.cost > f.cost"
    for (Q.push(Edge(-2, s)); !Q.empty(); ) {
      Edge e = Q.top(); Q.pop();
      if (p[e.dst] != -1) continue;
      p[e.dst] = e.src;
      FOR(f, g[e.dst]) if (RESIDUE(f->src, f->dst) > 0) {
        if (d[f->dst] > d[f->src] + RCOST(f->src, f->dst)) {
          d[f->dst] = d[f->src] + RCOST(f->src, f->dst);
          Q.push( Edge(f->src, f->dst, 0, d[f->dst]) );
        }
      }
    }
    if (p[t] == -1) break;

    Weight f = F;
    for (int u = t; u != s; u = p[u])
      f = min(f, RESIDUE(p[u], u));
    for (int u = t; u != s; u = p[u]) {
      total.first += f * cost[p[u]][u];
      flow[p[u]][u] += f; flow[u][p[u]] -= f;
    }
    F -= f;
    total.second += f;
    REP(u, n) h[u] += d[u];
  }
  return total;
}

int A[1000], B[1000];

void addEdge(Graph &g,int a,int b,int c,long long d){
	//cout << a << "=>" << b << " " << c << " (cost:" << d << ")" << endl;
	g[a].push_back(Edge(a,b,c,d));
	g[b].push_back(Edge(b,a,0,-d));
}
signed main(){
	int N;
	cin >> N;
	
	vector<int> u;
	for(int i = 0 ; i < N ; i++){
		cin >> A[i] >> B[i];
		u.push_back(A[i]);
		u.push_back(B[i]);
	}
	sort(u.begin(),u.end());
	u.erase(unique(u.begin(),u.end()),u.end());
	Graph g(u.size()+N+3);
	int s = g.size() - 1;
	int t = g.size() - 2;
	for(int i = 0 ; i < u.size() ; i++){
		addEdge(g,s,i,1,0);
		addEdge(g,i,t,1,0);
	}
	
	for(int i = 0 ; i < N ; i++){
		int a = lower_bound(u.begin(),u.end(),A[i])-u.begin();
		int b = lower_bound(u.begin(),u.end(),B[i])-u.begin();
		addEdge(g,a,u.size()+i,1,-B[i]);
		if( a != b ) addEdge(g,b,u.size()+i,1,-A[i]);
		addEdge(g,u.size()+i,t,1,0);
	}
	cout << -minimumCostFlow(g,s,t).first << endl;
}
  

Measured memory_bytes: 4696