#include <bits/stdc++.h>

#define FOR(i,a,b) for(int i= (a); i<((int)b); ++i)
#define RFOR(i,a) for(int i=(a); i >= 0; --i)
#define FOE(i,a) for(auto i : a)
#define ALL(c) (c).begin(), (c).end()
#define RALL(c) (c).rbegin(), (c).rend()
#define DUMP(x)  cerr << #x << " = " << (x) << endl;
#define SUM(x) std::accumulate(ALL(x), 0LL)
#define MIN(v) *std::min_element(v.begin(), v.end())
#define MAX(v) *std::max_element(v.begin(), v.end())
#define EXIST(v,x) (std::find(v.begin(), v.end(), x) != v.end())
#define BIT(n) (1LL<<(n))
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end());

typedef long long LL;
template<typename T> using V = std::vector<T>;
template<typename T> using VV = std::vector<std::vector<T>>;
template<typename T> using VVV = std::vector<std::vector<std::vector<T>>>;
template<class T> inline T ceil(T a, T b) { return (a + b - 1) / b; }
template<class T> inline void print(T x) { std::cout << x << std::endl; }
template<class T> inline bool inside(T y, T x, T H, T W) {return 0 <= y and y < H and 0 <= x and x < W; }
inline double distance(double y1, double x1, double y2, double x2) { return sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2)); }

const int INF = 1L << 30;
const double EPS = 1e-9;
const std::string YES = "YES", Yes = "Yes", NO = "NO", No = "No";
const std::vector<int> dy = { 0, 1, 0, -1 }, dx = { 1, 0, -1, 0 };    // 4近傍（右, 下, 左, 上）

using namespace std;

// 最小費用流
class PrimalDual {
    struct Edge {
        const int to;         // 行き先のノードid
        int flow;             // 流量
        const int cap;        // 容量
        const int cost;       // コスト
        const int rev;        // 逆辺のノードid
        const bool is_rev;    // 逆辺かどうか
        Edge(int to, int flow, int cap, int cost, int rev, bool is_rev) : to(to), flow(flow), cost(cost), cap(cap), rev(rev), is_rev(is_rev) {
            assert(this->cap >= 0);
        }
    };

    // s-tまでの最短経路
    struct Route {
        vector<int> dist;     // 最短距離
        vector<int> prevv;    // 前の頂点
        vector<int> preve;    // 直前の辺
        vector<int> h;        // ポテンシャル
        Route(vector<int> &dist, vector<int> &prevv, vector<int> &preve, vector<int> &h) : dist(dist), prevv(prevv), preve(preve), h(h) {}
    };

    const unsigned long V;       // 頂点数
    vector<vector<Edge>> graph;  // グラフの隣接リスト表現
    vector<int> h;             // ポテンシャル
    vector<int> dist;          // 最短距離
    vector<int> prevv, preve;  // 直前の頂点と辺

public:
    PrimalDual(unsigned long num_of_node) : V(num_of_node) {
        graph.resize(V);
        h.resize(V, 0);
        dist.resize(V);
        prevv.resize(V);
        preve.resize(V);
    }

// sからtへの流量fの最小費用流を求める
    // 流せない場合は-1を返す
    int min_cost_flow2(int s, int t, int f) {
        int res = 0;

        while (f > 0) {

            // ダイクストラ法を用いてhを更新する
            priority_queue<pair<int, int>, vector<pair<int, int>>, greater<pair<int, int>>> que;
            fill(dist.begin(), dist.end(), INT_MAX);
            dist[s] = 0;
            que.push(make_pair(0, s));
            while (not que.empty()) {
                pair<int, int> p = que.top();  // firstは最短距離, secondは頂点の番号
                que.pop();
                int v = p.second;
                if (dist[v] < p.first) {
                    continue;
                }
                for (int i = 0; i < graph[v].size(); ++i) {
                    Edge &e = graph[v][i];
                    if (e.cap - e.flow > 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(make_pair(dist[e.to], e.to));
                    }
                }
            }

            if (dist[t] == INT_MAX) {
                // これ以上流せない
                return res;
            }
            for (int v = 0; v < V; v++) {
                h[v] += dist[v];
            }
            // s-t間最短路に沿って目一杯流す
            int d = f;
            for (int v = t; v != s; v = prevv[v]) {
                d = min(d, graph[prevv[v]][preve[v]].cap - graph[prevv[v]][preve[v]].flow);
            }
            f -= d;
            res += d * h[t];
            for (int v = t; v != s; v = prevv[v]) {
                Edge &e = graph[prevv[v]][preve[v]];
                e.flow += d;
                graph[v][e.rev].flow -= d;
            }
        }
        return res;
    }

    // fromからtoへ向かう容量cap、コストcostの辺をグラフに追加する
    void add_edge(int from, int to, int cap, int cost) {
        graph[from].emplace_back(Edge(to, 0, cap, cost, graph[to].size(), false));
        graph[to].emplace_back(Edge(from, cap, cap, -cost, graph[from].size() - 1, true));
    }

    // sからtへの流量fの最小費用流を求める(流せない場合は-1)
    // O(F|E|log |V|)かO(F|V|^2)
    int min_cost_flow(int s, int t, int f) {
        int res = 0;

        while (f > 0) {
            Route route = dijkstra(s, t);
            vector<int> &dist = route.dist;
            vector<int> &prevv = route.prevv;
            vector<int> &preve = route.preve;
            vector<int> &h = route.h;

            // これ以上流せない
            if (dist[t] == INT_MAX) {
                return res;
                //return -1;
            }

            for (int v = 0; v < V; v++) {
                h[v] += dist[v];
            }

            // s-t間最短路に沿って目一杯流す
            int d = f;
            for (int v = t; v != s; v = prevv[v]) {
                int rest = graph[prevv[v]][preve[v]].cap - graph[prevv[v]][preve[v]].flow;
                d = min(d, rest);
            }
            f -= d;
            res += d * h[t];
            for (int v = t; v != s; v = prevv[v]) {
                Edge &e = graph[prevv[v]][preve[v]];
                e.flow += d;
                graph[v][e.rev].flow -= d;
            }
        }
        return res;
    }

    // sからtへの流量fの最小費用流(流せない場合は-1)
    // 負のコストがあってもいい
    // O(F|V||E|)
    int min_cost_flow_bellmanford(int s, int t, int f) {
        int res = 0;
        while (f > 0) {
            Route route = bellmanford(s, t);
            vector<int> &dist = route.dist;
            vector<int> &prevv = route.prevv;
            vector<int> &preve = route.preve;

            // これ以上流せない
            if (dist[t] == INT_MAX) {
                //return -1;
                return res; // 流せた分についての費用がほしいときはこっち
            }

            // s-t間最短路に沿って目一杯流す
            int d = f;
            for (int v = t; v != s; v = prevv[v]) {
                int rest = graph[prevv[v]][preve[v]].cap - graph[prevv[v]][preve[v]].flow;
                d = min(d, rest);
            }

            f -= d;
            res += d * dist[t];
            for (int v = t; v != s; v = prevv[v]) {
                Edge &e = graph[prevv[v]][preve[v]];
                e.flow += d;
                graph[v][e.rev].flow -= d;
            }
        }
        return res;
    }

    // 水の流れたエッジを取得する
    set<pair<int, int>> get_used_edges() {
        set<pair<int, int>> used_edges;
        for (int from = 0; from < this->graph.size(); ++from) {
            for (Edge edge : graph[from]) {
                int flow = edge.flow;
                bool is_rev = edge.is_rev;

                if (not is_rev and flow > 0) {
                    int to = edge.to;
                    used_edges.insert(make_pair(from , to));
                }
            }
        }
        return used_edges;
    }

private:
    // dijkstraでsからtへの最短ルートを求める
    Route dijkstra(int s, int t) {
        vector<int> dist(V, INT_MAX), prevv(V, 0), preve(V, 0), h(V, 0);

        priority_queue<pair<int, int>, vector<pair<int, int>>, greater<pair<int, int>>> que;
        dist[s] = 0;
        que.push(make_pair(0, s));
        while (not que.empty()) {
            pair<int, int> p = que.top();  // firstは最短距離, secondは頂点の番号
            que.pop();
            int v = p.second;
            if (dist[v] < p.first) {
                continue;
            }
            for (int i = 0; i < graph[v].size(); ++i) {
                Edge &e = graph[v][i];
                if (e.cap - e.flow > 0 and 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(make_pair(dist[e.to], e.to));
                }
            }
        }

        return Route(dist, prevv, preve, h);
    }

    // bellmanfordでsからtへの最短ルートを求める
    Route bellmanford(int s, int t) {
        vector<int> dist(V, INT_MAX), prevv(V, 0), preve(V, 0), h(V, 0);

        // ベルマンフォード法により、s-t間最短路を求める
        dist[s] = 0;
        bool update = true;
        while (update) {
            update = false;
            for (int v = 0; v < V; v++) {
                if (dist[v] == INT_MAX) continue;
                for (int i = 0; i < graph[v].size(); i++) {
                    Edge &e = graph[v][i];
                    int rest = e.cap - e.flow;
                    int new_cost = dist[v] + e.cost;
                    if (rest > 0 and dist[e.to] > new_cost) {
                        dist[e.to] = new_cost;
                        prevv[e.to] = v;
                        preve[e.to] = i;
                        update = true;
                    }
                }
            }
        }

        return Route(dist, prevv, preve, h);
    }

};

int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);

    int N;
    cin >> N;
    V<int> A(N), B(N);
    set<int> value_set;
    FOR(i, 0, N) {
        cin >> A[i] >> B[i];
        value_set.insert(A[i]);
        value_set.insert(B[i]);
    }
    V<int> v(ALL(value_set));

    int s = v.size() + N;
    int t = s + 1;
    int dummy = t + 1;
    PrimalDual pd(v.size() + N + 3);

    FOR(i, 0, v.size()) {
        pd.add_edge(s, i, 1, 0);
        pd.add_edge(i, dummy, INF, 0);
    }

    FOR(i, 0, v.size()) {
        FOR(j, 0, N) {
            int a = A[j], b = B[j];
            if (v[i] == a) {
                pd.add_edge(i, v.size() + j, 1, -b);
            }
            if (v[i] == b) {
                pd.add_edge(i, v.size() + j, 1, -a);
            }
        }
    }

    FOR(j, 0, N) {
        pd.add_edge(v.size() + j, t, 1, 0);
    }
    pd.add_edge(dummy, t, INF, 0);


    cout << -1 * pd.min_cost_flow2(s, t, N * 2) << endl;
    return 0;
}


Measured memory_bytes: 3892