#include <bits/stdc++.h>

using namespace std;

const int N = 5e3;

int n;
int l[N], r[N], match[N];
bitset<N> g[N], vis;
bool dfs(int u) {
  for (int v = (g[u] & ~vis)._Find_first(); v < n; v = (g[u] & ~vis)._Find_next(v)) {
    vis.set(v);
    if (match[v] == -1 || dfs(match[v])) { match[v] = u; return 1; }
  }
  return 0;
}
int ans;

int main() {
  scanf("%d", &n), fill_n(match, n, -1);
  for (int i = 0; i < n; ++i) scanf("%d%d", l + i, r + i), --l[i], --r[i];
  for (int i = 0; i < n; ++i)
    for (int j = 0; j < n; ++j)
      if (l[i] < l[j] && l[j] < r[i] && r[i] < r[j]) g[i].set(j);
  ans = n * 2;
  for (int i = 0; i < n; ++i) vis.reset(), ans -= dfs(i);
  printf("%d\n", ans);
}