#include<iostream>
using namespace std;
int n;
int l[10000], r[10000];
int ans = 0;
int c[1000];
int find(int x,int l[10000],int r[10000]) {
	for (int i = 0; i < 10000; i++) {
		if (l[i] == x || r[i] == x)return i;
		else return 0;
	}
}
int find2(int x, int c[10000]) {
	for (int i = 0; i < 10000; i++) {
		if (find(x,l,r) == 1)return 0;
		else return 1;
	}
}
int main() {
	cin >> n;
	for (int i = 0; i < n; i++) {
		cin >> l[i] >> r[i];
		if (l == 0 && r == 0);
		else {
			if(find(l[i],l,r)!=0||find(r[i],l,r))c[find(l[i], l, r)] = 1;
			if (find2(l[i], c) == 1 || find2(r[i], c) == 1)ans++, c[find(l[i], l, r)] = 1;
		}
	}
	cout << ans;
}