#include <cstdio>
#include <algorithm>


using namespace std;

long long x[1001],y[1001],n,nr1=0,nr2=0,k=0,l=0,ct1=0,ct2=0;

int main(){
	
	freopen("trapez.in","r",stdin);
	scanf("%lld",&n);
	
	for (int i=0;i<n;i++){
		scanf("%lld %lld",&x[i],&y[i]);
	}

	fclose(stdin);

	sort(x,x+n);
	sort(y,y+n);

	k=x[0];
	l=y[0];
	ct1++;
	ct2++;
	for (int i=1;i<n;i++){
		if(k!=x[i]){
			if(ct1==2)nr1++;
			k=x[i];
			ct1=1;
		}else ct1++;
		
		if(l!=y[i]){
			if(ct2==2)nr2++;
			l=y[i];
			ct2=1;
		}else ct2++;
	}
	
	freopen("trapez.out","w",stdout);
	printf("%lld",nr1/2+nr2/2);
	fclose(stdout);
	
	return 0;
}