import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

public class Main {
	static int n;
	static List<Set<Hen>> list;

	public static void main(String[] args) throws Exception {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		n = Integer.parseInt(br.readLine());
		int m = 200000;
		list = new ArrayList<>(m);
		for (int i = 0; i < m; i++) {
			list.add(new HashSet<>());
		}
		int[] in = new int[m];
		int[] out = new int[m];
		for (int i = 0; i < n; i++) {
			String[] sa = br.readLine().split(" ");
			Hen h = new Hen();
			h.a = Integer.parseInt(sa[0]) - 1;
			h.b = Integer.parseInt(sa[1]) - 1;
			if (h.a != h.b) {
				list.get(h.a).add(h);
				out[h.a]++;
				in[h.b]++;
			}
		}
		br.close();

		int s = -1;
		int t = -1;
		boolean even = false;
		for (int i = 0; i < m; i++) {
			if (in[i] != out[i]) {
				if (Math.abs(in[i] - out[i]) > 1) {
					System.out.println(0);
					return;
				}
				if (in[i] + 1 == out[i]) {
					if (s == -1) {
						s = i;
					} else {
						System.out.println(0);
						return;
					}
				} else {
					if (t == -1) {
						t = i;
					} else {
						System.out.println(0);
						return;
					}
				}
			}
		}
		if (s == -1) {
			for (int i = 0; i < m; i++) {
				if (out[i] > 0) {
					s = i;
					break;
				}
			}
			even = true;
		}
		if (even) {
			int ans = 0;
			for (int i = 0; i < m; i++) {
				if (!list.get(i).isEmpty()) {
					ans++;
				}
			}
			System.out.println(ans);
		} else {
			System.out.println(1);
		}
	}

	static class Hen {
		int a, b;
	}
}