#include<bits/stdc++.h>
using namespace std;
#define re register
#define inf 2147483647
const int N=4005;
const int M=500005;
struct edge{
    int nxt,v,val;
}s[M];
int n;
int c[N][N]={0};
int ans=0;
int S,T;
int hed[M];
int dis[M];
int q[M];
int h,t,cnt=-1;
int dfs(int u,int ep){
    if(u==T) return ep;//找到了，返回 
    int flow=0,tmp=0;
    for(int i=hed[u];~i;i=s[i].nxt){
        int v=s[i].v;
        if(dis[v]==dis[u]+1&&s[i].val>0){
            tmp=dfs(v,min(s[i].val,ep));
            if(!tmp) continue;
            ep-=tmp,flow+=tmp;
            s[i].val-=tmp,s[i^1].val+=tmp;//建立反向边
            if(!ep) break;//流量不够用？那就别增广了 
        }
    }
    return flow; 
} 
bool bfs(){//dinic的bfs预处理 
    memset(dis,-1,sizeof(dis));
    memset(q,0,sizeof(q));
    h=1,t=0;
    q[++t]=S;
    dis[S]=0;
    while(h<=t){
        
        int u=q[h];
        for(int i=hed[u];~i;i=s[i].nxt){
            int v=s[i].v;
            if(dis[v]!=-1||s[i].val<1) continue;
            dis[v]=dis[u]+1;
            q[++t]=v;
        }
        h++;
    }
    return dis[T]<0?0:1; 
}
void addege(int x,int y,int z){//加边
    cnt++;
    s[cnt].v=y;
    s[cnt].val=z;
    s[cnt].nxt=hed[x];
    hed[x]=cnt;
}
int main(){
    memset(hed,-1,sizeof(hed));
    scanf("%d",&n);
    for(re int i=1;i<=2*n;i++){
        int x,y;
        scanf("%d%d",&x,&y);
        addege(i,2*n+2*x-1,1);
        addege(2*n+2*x-1,i,0);
        addege(i,2*n+2*x,1);
        addege(2*n+2*x,i,0);
        addege(i,2*n+2*y-1,1);
        addege(2*n+2*y-1,i,0);
        addege(i,2*n+2*y,1);
        addege(2*n+2*y,i,0);
    }
    for(int i=1;i<=2*n;i++){
        addege(0,i,1);
        addege(i,0,0);
    }
    for(int i=2*n+1;i<=4*n;i++){
        addege(i,4*n+1,1);
        addege(4*n+1,i,0);
    }
    S=0,T=4*n+1; 
    while(bfs()){
        ans+=dfs(S,inf);
    }
    printf("%d\n",ans);
    return 0;
}