#include<bits/stdc++.h>
using namespace std;

int main(int argc, char const *argv[])
{
	int n;
	cin>>n;
	int count = 0;
	int arr[n][2];
	map<int,int>m;

	for (int i = 0; i < n; ++i)
	{
		/* code */
		
		
			/* code */
			cin>>arr[i][0]>>arr[i][1];
			if(m.find(arr[i][0]) != m.end()){
				m[arr[i][0]] += 1;
			}
			else
				m[arr[i][0]] = 1;

			if(m.find(arr[i][1]) != m.end()){
				m[arr[i][1]] += 1;
			}
			else
				m[arr[i][1]] = 1;
		
		count++;
	}

	int d;
	cin>>d;

	for (int i = 0; i < n ; ++i)
	{
		/* code */
		//cout<<m[arr[i][0]]<<" "<<m[arr[i][1]]<<"\n";
		if (m[arr[i][0]] > 2 || m[arr[i][1]] > 2)
			count--;
	}
	cout<<count<<"\n";


	return 0;
}