#include <bits/stdc++.h>
                                        #include<iostream>
                                        #include<cstdio>
                                        #include<vector>
                                        #include<queue>
                                        #include<map>
                                        #include<cstring>
                                        #include<string>
                                        #include <math.h>
                                        #include<algorithm>
                                    //    #include <boost/multiprecision/cpp_int.hpp>
                                        #include<functional>
                             //   #define int long long
                                        #define inf  1000000007
                                        #define pa pair<int,int>
                                        #define ll long long
                                        #define pal pair<double,pa>
                                        #define ppa pair<string,int>
                                        #define ppap pair<int,pa>
                                        #define ssa pair<string,int>
                                        #define  mp make_pair
                                        #define  pb push_back
                                        #define EPS (1e-12)
                                        #define equals(a,b) (fabs((a)-(b))<EPS)
                                  #define VI vector<int>
                                        using namespace std;
                                        
                                  class pas{
                                    	public:
                                    	int x,y;
                                    	pas(int x=0,int y=0):x(x),y(y) {}
                                    	pas operator + (pas p) {return pas(x+p.x,y+p.y);}
                                    	pas operator - (pas p) {return pas(x-p.x,y-p.y);}
                                    	pas operator * (int a) {return pas(x*a,y*a);}
                                    	pas operator / (int a) {return pas(x/a,y/a);}
                                    //	double absv() {return sqrt(norm());}
                                    	int norm() {return x*x+y*y;}
                                    	bool operator < (const pas &p) const{
                                   		return x != p.x ? x<p.x: y<p.y;
                                   	}
                                  //		bool operator < (const pas &p) const{
                                    //		return y != p.y ? y<p.y: x<p.x;
                                    //	}
                                    	bool operator == (const pas &p) const{
                                    		return x==p.x && y==p.y;
                                    	}
                                    };

                                        class Point{
                                        	public:
                                        	double x,y;
                                        	Point(double x=0,double y=0):x(x),y(y) {}
                                        	Point operator + (Point p) {return Point(x+p.x,y+p.y);}
                                        	Point operator - (Point p) {return Point(x-p.x,y-p.y);}
                                        	Point operator * (double a) {return Point(x*a,y*a);}
                                        	Point operator / (double a) {return Point(x/a,y/a);}
                                        	double absv() {return sqrt(norm());}
                                        	double norm() {return x*x+y*y;}
                                        	bool operator < (const Point &p) const{
                                        		return x != p.x ? x<p.x: y<p.y;
                                        	}
                                        	bool operator == (const Point &p) const{
                                        		return fabs(x-p.x)<EPS && fabs(y-p.y)<EPS;
                                        	}
                                        };
                                        typedef Point Vector;
                                 #define pl pair<int,pas>
                                        struct Segment{
                                        Point p1,p2;
                                        };
                                        
struct star{
Segment se[5];
};
                                         double dot(Vector a,Vector b){
                                        	return a.x*b.x+a.y*b.y;
                                        }
                                        double cross(Vector a,Vector b){
                                        	return a.x*b.y-a.y*b.x;
                                        }
                                    
            bool parareru(Point a,Point b,Point c,Point d){
            //	if(abs(cross(a-b,d-c))<EPS)cout<<"dd "<<cross(a-b,d-c)<<endl;
            	return abs(cross(a-b,d-c))<EPS;
            }
            double distance_ls_p(Point a, Point b, Point c) {
              if ( dot(b-a, c-a) < EPS ) return (c-a).absv();
              if ( dot(a-b, c-b) < EPS ) return (c-b).absv();
              return abs(cross(b-a, c-a)) / (b-a).absv();
            }
            bool is_intersected_ls(Segment a,Segment b) {
            	if(a.p1==b.p1||a.p2==b.p1||a.p1==b.p2||a.p2==b.p2) return false;
            	if(parareru((a.p2),(a.p1),(b.p1),(b.p2))&&parareru((a.p2),(a.p1),(b.p1),(b.p1))){
            //		cout<<"sss"<<endl;
            		if(dot(a.p1-b.p1,a.p1-b.p2)<EPS) return true;
            		if(dot(a.p2-b.p1,a.p2-b.p2)<EPS) return true;
            		if(dot(a.p1-b.p1,a.p2-b.p1)<EPS) return true;
            		if(dot(a.p1-b.p2,a.p2-b.p2)<EPS) return true;
            		return false;
            	}
              else return ( cross(a.p2-a.p1, b.p1-a.p1) * cross(a.p2-a.p1, b.p2-a.p1) < EPS ) && ( cross(b.p2-b.p1, a.p1-b.p1) * cross(b.p2-b.p1, a.p2-b.p1) < EPS );
            }
            double segment_len(Segment a){
            	
            	return (a.p1-a.p2).absv();
            }
            double segment_dis(Segment a,Segment b){
            	if(is_intersected_ls(a,b))return 0;
            	double r=distance_ls_p(a.p1, a.p2, b.p1);
            	r=min(r,distance_ls_p(a.p1, a.p2, b.p2));
            	r=min(r,distance_ls_p(b.p1, b.p2, a.p2));
            	r=min(r,distance_ls_p(b.p1, b.p2, a.p1));
            	return r;
            }
            Point intersection_ls(Segment a, Segment b) {
              Point ba = b.p2-b.p1;
              double d1 = abs(cross(ba, a.p1-b.p1));
              double d2 = abs(cross(ba, a.p2-b.p1));
              double t = d1 / (d1 + d2);
             
              return a.p1 + (a.p2-a.p1) * t;
            }
			pair<Point,Point> circle_intersection(Point c1,double r1,Point c2,double r2){
				double d=(c1-c2).absv();
				double h=(r1*r1-r2*r2+d*d)/2.0/d;
				double l=sqrt(r1*r1-h*h);
			//	cout<<d<<" "<<h<<" "<<l<<endl;
				Point asi=c1+(c2-c1)*h/((c2-c1).absv());
				Vector r1r2=(c2-c1)/((c2-c1).absv());
				Vector sui={r1r2.y,-r1r2.x};
			//	cout<<sui.x<<" "<<sui.y<<endl;
				pair<Point,Point> z=mp(asi+sui*l,asi-sui*l);
				if(z.first.x>z.second.x) swap(z.first,z.second);
				return z;
			}

int gcd(int x,int y){
	if(x<y) return gcd(y,x);
	if(x==y) return x;
	if(x%y==0) return y;
	return gcd(y,x%y);
}
 class pa2{
                                            public:
                                            int x,y;
                                            pa2(int x=0,int y=0):x(x),y(y) {}
                                            pa2 operator + (pa2 p) {return pa2(x+p.x,y+p.y);}
                                            pa2 operator - (pa2 p) {return pa2(x-p.x,y-p.y);}
                                            bool operator < (const pa2 &p) const{
                                                return x != p.x ? x<p.x: y<p.y;
                                            }
										 	 bool operator > (const pa2 &p) const{
                                                return x != p.x ? x>p.x: y>p.y;
                                            }
                                            bool operator == (const pa2 &p) const{
                                                return abs(x-p.x)==0 && abs(y-p.y)==0;
                                            }
                                            bool operator != (const pa2 &p) const{
                                                return !(abs(x-p.x)==0 && abs(y-p.y)==0);
                                            }
                                                 
                                         
                                        };
 typedef pair<int,int> P;
struct edge{ int to,cap,cost,rev;};
vector<edge> G[100010];
bool used[100010];
int h[100010],dist[100010],prevv[100010],preve[100010];
int V;//Vは頂点数

void add_edge(int from,int to,int cap,int cost){
	G[from].push_back( (edge){to,cap,cost,(int)G[to].size()} );
		G[to].push_back( (edge){from,0,-cost,(int)G[from].size()-1 });
}

int min_cost_flow(int s,int t,int f){
	int res=0;
	fill(h,h+V,0);
	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;
			for(int i=0;i<G[v].size();i++){
				edge &e=G[v][i];
				if(e.cap>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(P(dist[e.to],e.to));
				}
		}
	}
	if(dist[t]==inf) return -1;
	for(int v=0;v<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 a[1100],b[1100];
 set<int> se;
 map<int,int>ma;
 
/*　　　---memo---
add_edge(始点,終点,youryou ,コスト)で枝追加
min_cost_flow(始点,終点,ryou)でhiyouをintで返す
*/
     signed main(){
int n;
     	V=4000;
     	cin>>n;
     	for(int i=0;i<n;i++){
     		cin>>a[i]>>b[i];
     		se.insert(a[i]);
     		se.insert(b[i]);
     	}
     	int cnt=0;
     	for(auto it=se.begin();it!=se.end();it++){
     		ma[*it]=cnt;
     		cnt++;
     	}
     	int geta=0;
     	for(int i=0;i<n;i++){
     		add_edge(0,i+1,1,0);
     		int sai=max(a[i],b[i]);
     		geta+=sai;
     		add_edge(i+1,n+1,1,sai);
     		add_edge(i+1,n+2+ma[b[i]],1,sai-a[i]);
     		add_edge(i+1,n+2+ma[a[i]],1,sai-b[i]);
     	}
     	
     	for(int i=0;i<cnt;i++) add_edge(n+2+i,n+2+cnt,1,0);
     	add_edge(n+1,n+2+cnt,2000,0);
     	
     	cout<<geta-min_cost_flow(0,n+2+cnt,n)<<endl;
    
           	return 0;
           }


Measured memory_bytes: 6076