#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<ll, ll> l_l;
typedef pair<int, int> i_i;

//const ll mod = 1000000007;
const ll INF = 1e17;
template< typename flow_t, typename cost_t >
struct PrimalDual {
    const cost_t INF;

    struct edge {
        int to;
        flow_t cap;
        cost_t cost;
        int rev;
        bool isrev;
    };
    vector< vector< edge > > graph;
    vector< cost_t > potential, min_cost;
    vector< int > prevv, preve;

    PrimalDual(int V) : graph(V), INF(numeric_limits< cost_t >::max()) {}

    void add_edge(int from, int to, flow_t cap, cost_t cost) {
        graph[from].emplace_back((edge) {to, cap, cost, (int) graph[to].size(), false});
        graph[to].emplace_back((edge) {from, 0, -cost, (int) graph[from].size() - 1, true});
    }

    cost_t min_cost_flow(int s, int t, flow_t f) {
        int V = (int) graph.size();
        cost_t ret = 0;
        using Pi = pair< cost_t, int >;
        priority_queue< Pi, vector< Pi >, greater< Pi > > que;
        potential.assign(V, 0);
        preve.assign(V, -1);
        prevv.assign(V, -1);

        while(f > 0) {
            min_cost.assign(V, INF);
            que.emplace(0, s);
            min_cost[s] = 0;
            while(!que.empty()) {
                Pi p = que.top();
                que.pop();
                if(min_cost[p.second] < p.first) continue;
                for(int i = 0; i < graph[p.second].size(); i++) {
                    edge &e = graph[p.second][i];
                    cost_t nextCost = min_cost[p.second] + e.cost + potential[p.second] - potential[e.to];
                    if(e.cap > 0 && min_cost[e.to] > nextCost) {
                        min_cost[e.to] = nextCost;
                        prevv[e.to] = p.second, preve[e.to] = i;
                        que.emplace(min_cost[e.to], e.to);
                    }
                }
            }
            if(min_cost[t] == INF) return -1;
            for(int v = 0; v < V; v++) potential[v] += min_cost[v];
            flow_t addflow = f;
            for(int v = t; v != s; v = prevv[v]) {
                addflow = min(addflow, graph[prevv[v]][preve[v]].cap);
            }
            f -= addflow;
            ret += addflow * potential[t];
            for(int v = t; v != s; v = prevv[v]) {
                edge &e = graph[prevv[v]][preve[v]];
                e.cap -= addflow;
                graph[v][e.rev].cap += addflow;
            }
       }
       return ret;
    }

    void output() {
        for(int i = 0; i < graph.size(); i++) {
            for(auto &e : graph[i]) {
                if(e.isrev) continue;
                auto &rev_e = graph[e.to][e.rev];
                cout << i << "->" << e.to << " (flow: " << rev_e.cap << "/" << rev_e.cap + e.cap << ")" << endl;
            }
        }
    }
};

vector<int> cmp;
int N;
int A[1005], B[1005];

int main() {
    //cout.precision(10);
    cin.tie(0);
    ios::sync_with_stdio(false);
    PrimalDual<ll, ll> graph(3005);
    cin >> N;
    ll ans = 0;
    for(int i = 0; i < N; i++) {
        cin >> A[i] >> B[i];
        cmp.push_back(A[i]);
        cmp.push_back(B[i]);
        if(A[i] < B[i]) swap(A[i], B[i]);
        ans += A[i];
    }
    sort(cmp.begin(), cmp.end());
    cmp.erase(unique(cmp.begin(), cmp.end()), cmp.end());
    int s = 3003;
    int t = 3004;
    for(int i = 0; i < cmp.size(); i++) {
        graph.add_edge(N + i, t, 1, 0);
    }
    for(int i = 0; i < N; i++) {
        graph.add_edge(s, i, 1, 0);
        auto itr = lower_bound(cmp.begin(), cmp.end(), A[i]);
        int idx = distance(cmp.begin(), itr);
        graph.add_edge(i, N + idx, 1, A[i] - B[i]);
        itr = lower_bound(cmp.begin(), cmp.end(), B[i]);
        idx = distance(cmp.begin(), itr);
        graph.add_edge(i, N + idx, 1, 0);
        graph.add_edge(i, t, 1, A[i]);
    }
    cout << ans - graph.min_cost_flow(s, t, N) << endl;
    return 0;
}


Measured memory_bytes: 3704