#include <iostream>
#include <bitset>

using namespace std;
using Pii = pair<int, int>;

const int kN = 1e4 + 1;

int n, p[kN], ans;
Pii a[kN];
bitset<kN> e[kN], v;

bool F(int x) {
  for (int i = (v & e[x])._Find_first(); i <= 2 * n; i = (v & e[x])._Find_next(i)) {
    v[i] = 0;
    if (!p[i] || F(p[i])) {
      p[i] = x;
      return 1;
    }
  }
  return 0;
}

int main() {
  ios::sync_with_stdio(0), cin.tie(0);
  cin >> n;
  for (int i = 1; i <= n; ++i) {
    cin >> a[i].first >> a[i].second;
  }
  for (int i = 1; i <= n; ++i) {
    for (int j = 1; j <= n; ++j) {
      if (a[i].first < a[j].first && a[j].first < a[i].second && a[i].second < a[j].second) {
        e[a[j].first][a[i].second] = 1;
      }
    }
  }
  for (int i = 1; i <= 2 * n; ++i) {
    v.set(), ans += F(i);
  }
  cout << n * 2 - ans;
  return 0;
}