/* -*- coding: utf-8 -*-
 *
 * 1605.cc:  No.1605 Matrix Shape - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 200000;
const int MAX_M = 200000;

/* typedef */

typedef vector<int> vi;
typedef queue<int> qi;
typedef pair<int,int> pii;

/* global variables */

pii ps[MAX_N];
vi nbrs[MAX_M];
int xs[MAX_N * 2], ies[MAX_M], oes[MAX_M];
bool used[MAX_M];

/* subroutines */

int bfd(int st) {
  used[st] = true;
  int c = 1;

  qi q;
  q.push(st);

  while (! q.empty()) {
    int u = q.front(); q.pop();
    for (auto v: nbrs[u])
      if (! used[v]) {
	used[v] = true;
	c++;
	q.push(v);
      }
  }

  return c;
}

/* main */

int main() {
  int n;
  scanf("%d", &n);

  int m = 0;
  for (int i = 0; i < n; i++) {
    int h, w;
    scanf("%d%d", &h, &w);
    h--, w--;
    ps[i] = pii(h, w);
    xs[m++] = h, xs[m++] = w;
  }
  sort(xs, xs + m);
  m = unique(xs, xs + m) - xs;
  //printf("m=%d\n", m);

  for (int i = 0; i < n; i++) {
    int hi = lower_bound(xs, xs + m, ps[i].first) - xs;
    int wi = lower_bound(xs, xs + m, ps[i].second) - xs;
    ps[i] = pii(hi, wi);
    ies[wi]++, oes[hi]++;
    nbrs[hi].push_back(wi);
  }

  int stc = 0, glc = 0, sti = -1, gli = -1;;
  for (int i = 0; i < m; i++) {
    if (ies[i] + 1 == oes[i]) stc++, sti = i;
    else if (oes[i] + 1 == ies[i]) glc++, gli = i;
    else if (ies[i] != oes[i]) {
      puts("0"); return 0;
    }
  }

  if (stc > 1 || glc > 1 || stc != glc) { puts("0"); return 0; }

  int c = bfd((stc > 0) ? sti : 0);
  //printf("c=%d, m=%d\n", c, m);
  if (c < m) { puts("0"); return 0; }

  printf("%d\n", (stc > 0) ? 1 : m);
  return 0;
}