#ifndef LOCAL
    #pragma GCC optimize("Ofast")
#endif
#include <cassert>
#include <iostream>
#include <algorithm>
#include <functional>
#include <queue>
#include <deque>
#include <stack>
#include <list>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <complex>
#include <iomanip>
#include <bitset>
#include <random>

using namespace std;
using i64 = int_fast64_t;
using db = double;
using ldb = long double;
using pii = pair<int, int>;
using pli = pair<int_fast64_t, int>;
using pll = pair<int_fast64_t, int_fast64_t>;
using pdi = pair<double, int>;
using pdd = pair<double, double>;
template <class T> using vct = vector<T>;
template <class T> using heap = priority_queue<T>;
template <class T> using minheap = priority_queue<T, vector<T>, greater<T>>;
template <class T> constexpr T inf = numeric_limits<T>::max() / (T)16;
constexpr int dx[9] = {1, 0, -1, 0, 1, -1, -1, 1, 0};
constexpr int dy[9] = {0, 1, 0, -1, 1, 1, -1, -1, 0};
constexpr long double Pi = 3.1415926535897932384626433832795028;
constexpr long double Golden = 1.61803398874989484820;
constexpr long double eps = 1e-15;

#define iostream_untie true
#define mod 1000000007LL
#define stdout_precision 10
#define stderr_precision 6
#define itrep(i,v) for(auto i = begin(v); i != end(v); ++i)
#define ritrep(i,v) for(auto i = rbegin(v); i != rend(v); ++i)
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define rrep(i,n) for(int i = (n) - 1; i >= 0; --i)
#define all(v) begin(v), end(v)
#define rall(v) rbegin(v), rend(v)
#define fir first
#define sec second
#define u_map unordered_map
#define u_set unordered_set
#define l_bnd lower_bound
#define u_bnd upper_bound
#define rsz resize
#define ers erase
#define emp emplace
#define emf emplace_front
#define emb emplace_back
#define pof pop_front
#define pob pop_back
#define mkp make_pair
#define mkt make_tuple
#define popcnt __builtin_popcount

namespace setup {
    struct setupper {
        setupper() {
            if(iostream_untie) {
                ios::sync_with_stdio(false);
                std::cin.tie(nullptr);
                std::cout.tie(nullptr);
                std::cerr.tie(nullptr);
            }
            std::cout << fixed << setprecision(stdout_precision);
            std::cerr << fixed << setprecision(stderr_precision);
    #ifdef LOCAL
            if(!freopen("input.txt","rt",stdin)) {
                std::cerr << "Failed to open the input file.\n"; std::exit(EXIT_FAILURE);
            }
            // if(!freopen("output.txt","wt",stdout)) {
            //     cerr << "Failed to open the output file.\n"; exit(EXIT_FAILURE);
            // }
            // std::cerr << "\n---stderr---\n";
            // auto print_atexit = []() {
            //     std::cerr << "Exec time : " << clock() / (double)CLOCKS_PER_SEC * 1000.0 << "ms\n";
            //     std::cerr << "------------\n";
            // };
            // atexit((void(*)())print_atexit);
            // atexit((void(*)())fclose(stdin));
    #endif
        }
    } __setupper;
}

namespace std {
    template <class RAitr> void rsort(RAitr __first, RAitr __last) {
        sort(__first, __last, greater<>());
    }
    template <class T> void hash_combine(size_t &seed, T const &key) {
        seed ^= hash<T>()(key) + 0x9e3779b9 + (seed << 6) + (seed >> 2);
    }
    template <class T, class U> struct hash<pair<T,U>> {
        size_t operator()(pair<T,U> const &pr) const
        {
            size_t seed = 0;
            hash_combine(seed,pr.first);
            hash_combine(seed,pr.second);
            return seed;
        }
    };
    template <class Tup, size_t index = tuple_size<Tup>::value - 1> struct hashval_calc {
        static void apply(size_t& seed, Tup const& tup) {
            hashval_calc<Tup, index - 1>::apply(seed, tup);
            hash_combine(seed,get<index>(tup));
        }
    };
    template <class Tup> struct hashval_calc<Tup,0> {
        static void apply(size_t& seed, Tup const& tup) {
            hash_combine(seed,get<0>(tup));
        }
    };
    template <class ...T> struct hash<tuple<T...>> {
        size_t operator()(tuple<T...> const& tup) const
        {
            size_t seed = 0;
            hashval_calc<tuple<T...>>::apply(seed,tup);
            return seed;
        }
    };
}

template <class T, class U> istream &operator>> (istream &s, pair<T,U> &p) { return s >> p.first >> p.second; }
template <class T, class U> ostream &operator<< (ostream &s, const pair<T,U> p) { return s << p.first << " " << p.second; }
template <class T> ostream &operator<< (ostream &s, const vector<T> &v) {
    for(size_t i = 0; i < v.size(); ++i) s << (i ? " " : "") << v[i]; return s;
}
#define dump(...) cerr << " [ " << __LINE__ << " : " << __FUNCTION__ << " ] " << #__VA_ARGS__ << " : ";\
dump_func(__VA_ARGS__)
template <class T> void dump_func(T x) { cerr << x << '\n'; }
template <class T,class ...Rest> void dump_func(T x, Rest ... rest) { cerr << x << ","; dump_func(rest...); }
template <class T = i64> T read() { T x; return cin >> x, x; }
template <class T> void write(T x) { cout << x << '\n'; }
template <class T, class ...Rest> void write(T x, Rest ... rest) { cout << x << ' '; write(rest...); }
void writeln() {}
template <class T, class ...Rest> void writeln(T x, Rest ... rest) { cout << x << '\n'; writeln(rest...); }
#define esc(...) writeln(__VA_ARGS__), exit(0)

namespace updater {
    template <class T> static void add(T &x, const T &y) { x += y; }
    template <class T> static void ext_add(T &x, const T &y, size_t w) { x += y * w; }
    template <class T> static void mul(T &x, const T &y) { x *= y; }
    template <class T> static void ext_mul(T &x, const T &y, size_t w) { x *= (T)pow(y,w); }
    template <class T> static bool chmax(T &x, const T &y) { return x < y ? x = y,true : false; }
    template <class T> static bool chmin(T &x, const T &y) { return x > y ? x = y,true : false; }
};
using updater::add;
using updater::chmax;
using updater::chmin;

template <class T> constexpr T minf(const T &x, const T &y) { return min(x,y); }
template <class T> constexpr T maxf(const T &x, const T &y) { return max(x,y); }
constexpr bool bit(i64 n, int e) { return (n >> e) & 1; }
constexpr int_fast64_t mask(int_fast64_t n, int e) { return n & ((1 << e) - 1); }
constexpr int ilog(int_fast64_t x, int_fast64_t b = 2) { return x ? 1 + ilog(x / b, b) : -1; }
template <class F> int_fast64_t binry(int_fast64_t ok, int_fast64_t ng, const F &fn) {
    while (abs(ok - ng) > 1) {
        int_fast64_t mid = (ok + ng) / 2;
        (fn(mid) ? ok : ng) = mid;
    }
    return ok;
}
template <class A, size_t N, class T> void init(A (&array)[N], const T &val) { fill((T*)array,(T*)(array + N),val); }
template <class T> vector<int> cmprs(const vector<T> &v) {
    vector<T> tmp = v; vector<int> ret;
    sort(begin(tmp),end(tmp));
    tmp.erase(unique(begin(tmp),end(tmp)), end(tmp));
    for(T i : v) ret.emplace_back(lower_bound(begin(tmp),end(tmp),i) - begin(tmp));
    return ret;
}
template <class T> vector<int> cmprs(const T *__first, const T *__last) {
    return cmprs(vector<T>(__first, __last));
}
template <class F> void for_subset(uint_fast64_t s, const F &fn) {
    uint_fast64_t tmp = s;
    do { fn(tmp); } while((--tmp &= s) != s);
}



/* The main code follows. */


template <class cost_t = int_fast64_t, class cap_t = int_fast64_t>
struct Flow {
    struct edge { int to; cost_t cost; cap_t cap; edge *rev; };
    size_t V,E;
    bool neg_edge_exist;
    vector<vector<edge>> adj;

    Flow(size_t _V) : V(_V),E(),neg_edge_exist() {
        adj.resize(V * 2);
        if(V <= 5e3) for(size_t v = 0; v != V * 2; ++v) adj[v].reserve(V * 2);
    }

    void add_edge(int from, int to, cost_t cost, cap_t cap) {
        adj[from].emplace_back((edge){ to, cost, cap, nullptr });
        adj[to].emplace_back((edge){ from, -cost, 0, nullptr });
        adj[from].back().rev = &(adj[to].back());
        adj[to].back().rev = &(adj[from].back());
        ++E; if(cost < 0) neg_edge_exist = true;
    }

    vector<cost_t> Dijkstra(int s) {
        vector<cost_t> dist(V,inf<cost_t>);
        priority_queue<pair<cost_t,int>,vector<pair<cost_t,int>>,greater<pair<cost_t,int>>> que;
        que.emplace(dist[s] = 0, s);
        while(!que.empty()) {
            auto p = que.top(); que.pop();
            int v = p.second;
            if(dist[v] < p.first) continue;
            for(edge &e : adj[v]) {
                if(e.cap > 0 && dist[v] + e.cost < dist[e.to]) que.emplace(dist[e.to] = dist[v] + e.cost, e.to);
            } 
        }
        return dist;
    }

    struct Fold_Fulkerson_exe {
        Flow &F;
        vector<bool> used;

        Fold_Fulkerson_exe(Flow &_F) : F(_F) {
            used.resize(F.V);
        }

        cap_t dfs(int v, int t, cap_t f) {
            if(v == t) return f;
            used[v] = true;
            for(edge &e : F.adj[v]) {
                if(!used[e.to] && e.cap > 0) {
                    cap_t d = dfs(e.to,t,min(f,e.cap));
                    if(d > 0) {
                        e.cap -= d;
                        e.rev->cap += d;
                        return d;
                    }
                }
            }
            return 0;
        }

        cap_t max_flow(int s, int t) {
            cap_t flow = 0,f;
            while(true) {
                fill(begin(used),end(used),false);
                if((f = dfs(s,t,numeric_limits<cap_t>())) > 0) flow += f;
                else break;
            }
            return flow;
        }
    };

    cap_t Fold_Fulkerson(int s, int t) { return Fold_Fulkerson_exe(*this).max_flow(s,t); }
    
    struct Dinic_exe {
        Flow &F;
        vector<int> level,itr;

        Dinic_exe(Flow &_F) : F(_F) {
            level.resize(F.V), itr.resize(F.V);
        }

        void bfs(int s) {
            fill(begin(level),end(level),-1);
            queue<int> que;
            level[s] = 0;
            que.emplace(s);
            while(!que.empty()) {
                int v = que.front(); que.pop();
                for(edge &e : F.adj[v]) {
                    if(e.cap > 0 && level[e.to] < 0) {
                        level[e.to] = level[v] + 1;
                        que.emplace(e.to);
                    }
                } 
            }
        }

        cap_t dfs(int v, int t, cap_t f) {
            if(v == t) return f;
            for(int &i = itr[v]; i != F.adj[v].size(); ++i) {
                edge &e = F.adj[v][i];
                if(e.cap > 0 && level[v] < level[e.to]) {
                    cap_t d = dfs(e.to, t, min(f,e.cap));
                    if(d > 0) {
                        e.cap -= d;
                        e.rev->cap += d;
                        return d;
                    }
                }
            }
            return 0;
        }

        cap_t max_flow(int s, int t) {
            cap_t flow = 0,f;
            while(true) {
                bfs(s);
                if(level[t] < 0) return flow;
                fill(begin(itr),end(itr),0);
                while((f = dfs(s,t,inf<cap_t>)) > 0) flow += f;
            }
        }
    };

    cap_t Dinic(int s, int t) { return Dinic_exe(*this).max_flow(s,t); }

    struct Primal_Dual_exe {
        Flow &F;
        vector<cost_t> dist,h;
        vector<int> prev_v;
        vector<edge*> prev_e;

        Primal_Dual_exe(Flow &_F) : F(_F) {
            dist.resize(F.V), h.resize(F.V), prev_v.resize(F.V), prev_e.resize(F.V);
        }

        bool Dijkstra(int s, int t) {
            priority_queue<pair<cost_t,int>,vector<pair<cost_t,int>>,greater<pair<cost_t,int>>> que;
            fill(begin(dist),end(dist),inf<cost_t>);
            que.emplace(dist[s] = 0, s);
            while(!que.empty()) {
                cost_t cs; int v;
                tie(cs,v) = que.top();
                que.pop();
                if(cs > dist[v]) continue;
                for(edge &e : F.adj[v]) {
                    if(e.cap > 0 && dist[v] + h[v] + e.cost < dist[e.to] + h[e.to]) {
                        que.emplace(dist[e.to] = dist[v] + h[v] - h[e.to] + e.cost, e.to);
                        prev_v[e.to] = v;
                        prev_e[e.to] = &e;
                    }
                }
            } 
            if(dist[t] >= inf<cost_t>) return false;
            for(int v = 0; v < F.V; ++v) h[v] += dist[v];
            return true;
        }

        cost_t min_cost_flow(int s, int t, cap_t f) {
            cost_t res = 0;
            fill(begin(h),end(h),0);
            while(f > 0) {
                if(!Dijkstra(s,t)) return inf<cost_t>;
                cap_t d = f;
                for(int v = t; v != s; v = prev_v[v]) d = min(d, prev_e[v]->cap);
                f -= d;
                res += d * h[t];
                for(int v = t; v != s; v = prev_v[v]) {
                    prev_e[v]->cap -= d;
                    prev_e[v]->rev->cap += d;
                }
            }
            return res;
        }
    };

    cost_t Primal_Dual(int s, int t, cap_t f) {
        cost_t corr = 0;
        if(neg_edge_exist) {
            neg_edge_exist = false;
            int _s = V++;
            int _t = V++;
            add_edge(_s,s,0,f);
            add_edge(t,_t,0,f);
            s = _s, t = _t;
            for(int v = 0; v < V; ++v) {
                for(edge &e : adj[v]) {
                    if(e.cost < 0) {
                        f += e.cap;
                        add_edge(s,e.to,0,e.cap);
                        add_edge(v,t,0,e.cap);
                        corr += e.cap * e.cost;
                        e.rev->cap += e.cap;
                        e.cap = 0;
                    }
                }
            }
        }
        return Primal_Dual_exe(*this).min_cost_flow(s,t,f) + corr;
    } 
};

int n;
pii pairs[2010];
int values[2010];
u_map<int,int> vtoi;
int itov[2010];

signed main() {
    cin>>n;
    rep(i,n) {
        cin>>pairs[i].fir>>pairs[i].sec;
        values[i*2]=pairs[i].fir;
        values[i*2+1]=pairs[i].sec;
    }
    auto cmp=cmprs(values,values+n*2);
    rep(i,n*2) {
        itov[cmp[i]]=values[i];
        vtoi[values[i]]=cmp[i];
    }
    int vnum=n*3+2;
    Flow<> flow(vnum);
    int s=vnum-2;
    int t=vnum-1;
    rep(i,n) {
        flow.add_edge(i,t,0,1);
        int fi=n+vtoi[pairs[i].fir];
        int se=n+vtoi[pairs[i].sec];
        flow.add_edge(fi,i,-pairs[i].sec,1);
        flow.add_edge(se,i,-pairs[i].fir,1);
    }
    for(int i=0; itov[i]!=0; ++i) {
        flow.add_edge(s,i+n,0,1);
    }
    flow.add_edge(s,t,0,inf<int>);
    esc(-flow.Primal_Dual(s,t,n));
}



Measured memory_bytes: 27780