#include "bits/stdc++.h"
#include<unordered_map>
#include<unordered_set>
#pragma warning(disable:4996)
using namespace std;
using ld = long double;
template<class T>
using Table = vector<vector<T>>;
const ld eps=1e-9;

// < "D:\D_Download\Visual Studio 2015\Projects\programing_contest_c++\Debug\a.txt"

struct Compress {
	map<int, int>mp;
	map<int, int>revmp;

	Compress(vector<int>vs) {
		sort(vs.begin(), vs.end());
		vs.erase(unique(vs.begin(), vs.end()), vs.end());
		for (int i = 0; i < vs.size(); ++i) {
			mp[vs[i]] = i;
			revmp[i] = vs[i];
		}
	}
};
typedef long long  Weight;
struct Edge {
	int src, dest;
	int cap, rev;
	Weight weight;
	bool operator < (const Edge &rhs) const { return weight > rhs.weight; }
};

const int V = 4000;
typedef vector<Edge> Edges;
typedef vector<Edges> Graph;
typedef vector<Weight> Array;
typedef vector<Array> Matrix;
Weight h[V];                //??????????????£???
Weight dist[V];             //???????????¢
int prevv[V], preve[V];  //??´???????????¨??????

void add_edge(Graph &g, int src, int dest, int cap, int weight) {
	g[src].push_back(Edge { src, dest, cap, (int)g[dest].size(), weight });
	g[dest].push_back(Edge { dest, src, 0, (int)g[src].size() - 1, -weight });
}
#define REP(i,n) for(int i=0;i<(int)n;++i)
#define FOR(i,c) for(auto i=(c).begin();i!=(c).end();++i)
#define ALL(c) (c).begin(), (c).end()
const int INF = 2147483647;
const long long int L_INF = 9223372036854775807;
Weight min_cost_flow(Graph &g, int s, int t, int f) {
	Weight res = 0;
	memset(h, 0, sizeof(h));
	typedef pair<Weight, int> P;
	while (f > 0) {
		priority_queue<P, vector<P>, greater<P> > que;
		fill(dist, dist + V, 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;
			REP(i, g[v].size()) {
				Edge &e = g[v][i];
				if (e.cap > 0 && dist[e.dest] > dist[v] + e.weight + h[v] - h[e.dest]) {
					dist[e.dest] = dist[v] + e.weight + h[v] - h[e.dest];
					prevv[e.dest] = v;
					preve[e.dest] = i;
					que.push(P(dist[e.dest], e.dest));
				}
			}
		}
		if (dist[t] == INF) return -1;
		REP(v, 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]) {
			Edge &e = g[prevv[v]][preve[v]];
			e.cap -= d;
			g[v][e.rev].cap += d;
		}
	}
	return res;
}
int main() {
	int N; cin >> N;
	vector<int>vs;
	vector<pair<long long int,long long  int>>ps;
	for (int i = 0; i < N; ++i) {
		long long int a, b; cin >> a >> b;
		ps.emplace_back(a, b);
		vs.push_back(a);
		vs.push_back(b);
	}
	Compress cp(vs);

	const int start = 0;
	const int snode = start + 1;
	const int he = snode + N;
	const int goal = he + 2*N;
	Graph g(goal+1);
	for (int i = 0; i < N; ++i) {
		add_edge(g,start, snode + i, 1, 0);
	}
	for (int i = 0; i < N; ++i) {
		add_edge(g, snode+i, he + cp.mp[ps[i].second], 1, 1000000 - ps[i].first);
		add_edge(g, snode + i, he + cp.mp[ps[i].first], 1, 1000000 - ps[i].second);
		add_edge(g, snode + i, goal, 1, 1000000);
	}
	for (int i = 0; i < 2*N; ++i) {
		add_edge(g, he + i, goal, 1, 0);
	}
	auto p = min_cost_flow(g, start, goal,N);
	long long int ans = 1000000 * N - p;
	cout << ans << endl;
	return 0;
}

Measured memory_bytes: 3748