#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <functional>
#include <iostream>
#include <limits>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

using namespace std;

using Int = long long;

template <class T1, class T2> ostream &operator<<(ostream &os, const pair<T1, T2> &a) { return os << "(" << a.first << ", " << a.second << ")"; };
template <class T> ostream &operator<<(ostream &os, const vector<T> &as) { const int sz = as.size(); os << "["; for (int i = 0; i < sz; ++i) { if (i >= 256) { os << ", ..."; break; } if (i > 0) { os << ", "; } os << as[i]; } return os << "]"; }
template <class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cerr << *i << " "; cerr << endl; }
template <class T> bool chmin(T &t, const T &f) { if (t > f) { t = f; return true; } return false; }
template <class T> bool chmax(T &t, const T &f) { if (t < f) { t = f; return true; } return false; }
#define COLOR(s) ("\x1b[" s "m")


/*
  need to erase all concave vertices
  connecting two concave vertices is good
  ind. set of segments
  
  yoko segment: intersects with all tate segments in the interval
  
  bipartite matching: for each tate, greedily take yoko
*/

int N;
vector<int> A[2];

int main() {
  for (; ~scanf("%d", &N); ) {
    A[0].resize(N);
    A[1].resize(N);
    for (int i = 0; i < N; ++i) {
      scanf("%d%d", &A[0][i], &A[1][i]);
    }
    
    int cave = 0, segm = 0;
    vector<vector<int>> yoko(N + 1);
    for (int h = 0; h < 2; ++h) {
      for (int i = 1; i < N; ++i) {
        if (A[h][i - 1] != A[h][i]) {
          ++cave;
        }
      }
      vector<int> stack;
      for (int i = 0; i < N; ++i) {
        for (; stack.size() && A[h][stack.back()] > A[h][i]; stack.pop_back()) {}
        if (stack.size() && A[h][stack.back()] == A[h][i]) {
          const int j = stack.back() + 1;
          if (j < i) {
// cerr<<"yoko "<<h<<" ["<<j<<", "<<i<<"]"<<endl;
            ++segm;
            yoko[j].push_back(i);
          }
          stack.pop_back();
        }
        stack.push_back(i);
      }
    }
    
    priority_queue<int, vector<int>, greater<int>> que;
    int ma = 0;
    for (int i = 1; i < N; ++i) {
      for (const int j : yoko[i]) {
        que.push(j);
      }
      if (A[0][i - 1] != A[0][i] && A[1][i - 1] != A[1][i]) {
        ++segm;
        for (; que.size(); ) {
          const int j = que.top();
          que.pop();
          if (i <= j) {
            ++ma;
            break;
          }
        }
      }
    }
// cerr<<"cave = "<<cave<<", segm = "<<segm<<", ma = "<<ma<<endl;
    const int ans = cave - (segm - ma);
    printf("%d\n", ans);
  }
  return 0;
}