/*
If the radiance of a thousand suns were to burst into the sky?
...that would be like the splendor of the mighty one.
*/
#include <bits/stdc++.h>
#define pii pair<int, int>
#define mp(x, y) make_pair(x, y)
#define all(v) (v).begin(), (v).end()
using i128 = __int128;
using i64 = long long;
using u64 = unsigned long long;

const int maxn = 5010;
std::bitset<maxn> to[maxn];

inline void solve() {
  int n; std::cin >> n;
  std::vector<int> l(n + 1), r(n + 1);
  for (int i = 1; i <= n; i++) std::cin >> l[i] >> r[i];

  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= n; j++) if (l[i] < l[j] && l[j] < r[i] && r[i] < r[j])
      to[i][j] = true;

  std::vector<int> match(n + 1);
  auto bfs = [&](int u) {
    std::queue<int> que;
    std::bitset<maxn> vis;
    std::vector<int> prex(n + 1), prey(n + 1);
    vis.set(), que.push(u);
    int v = -1;
    while (!que.empty()) {
      int x = que.front(); que.pop();
      std::bitset<maxn> tmp = vis & to[x];
      for (int y = tmp._Find_first(); y <= n; y = tmp._Find_next(y)) {
        int z = match[y]; vis[y] = 0;
        if (!z) { match[y] = x, v = x; break; }
        que.push(z), prex[z] = x, prey[z] = y;
      }
      if (~v) break;
    }
    if (v == -1) return 0;
    while (v != u) match[prey[v]] = prex[v], v = prex[v];
    return 1;
  };

  int res = 2 * n;
  for (int i = 1; i <= n; i++) res -= bfs(i);
  std::cout << res << "\n";
}

int main() {
  std::ios::sync_with_stdio(false);
  std::cin.tie(0), std::cout.tie(0);

  int T = 1;
  // std::cin >> T;
  while (T--) solve();
  return 0;
}