#include <bits/stdc++.h>
using namespace std;
int c1,c2,n;//c1 2head-1tail c2 1head-2tail
map<string,int>wei;
map<string,int>tou;
int main(){
	cin>>n;
	for(int i=1;i<=n;i++){
		string s1,s2,s3,s4;
		cin>>s1>>s2>>s3>>s4;
		tou[s1]++,wei[s4]++;
		//cout<<s1<<" "<<tou[s1]<<" "<<s4<<" "<<wei[s4]<<"\n";
		if(tou[s1]==2&&wei[s1]==1){c1++,tou[s1]-=2,wei[s1]-=1;}
		if(tou[s4]==2&&wei[s4]==1){c1++,tou[s4]-=2,wei[s4]-=1;}
		if(tou[s1]==1&&wei[s1]==2){c2++,tou[s1]-=1,wei[s1]-=2;}
		if(tou[s4]==1&&wei[s4]==2){c2++,tou[s4]-=1,wei[s4]-=2;}
	}
	cout<<min(c1/2,c2/2);
	return 0;
}