#include <bits/stdc++.h>
#define pii pair<int, int>
#define fi first
#define se second
#define MP make_pair
#define ep emplace
#define eb emplace_back
//#define int long long
#define rep(i, j, k) for (int i = j; i <= k; i++)
#define per(i, j, k) for (int i = j; i >= k; i--)
typedef double db;
typedef long double ldb;
typedef long long ll;
typedef __int128 lll;
typedef unsigned long long ull;
typedef unsigned int ui;
using namespace std;

int read() {
	int s = 0, f = 1;
	char c = getchar();
	while (c < '0' || c > '9') f ^= (c == '-'), c = getchar();
	while (c >= '0' && c <= '9') s = s * 10 + c - '0', c = getchar();
	return f ? s : -s;
}
const int inf = 0x3f3f3f3f;
int n, s, t, tot = 1, head[200005], dis[200005], now[200005], rt, cnt;
struct edge { int to, nxt, flow; } e[200005];
void addedge(int u, int v, int w) {
	e[++tot] = edge{ v, head[u], w }; head[u] = tot;
	e[++tot] = edge{ u, head[v], 0 }; head[v] = tot;
}
bool bfs() {
	memset(dis, 0x3f, sizeof dis);
	memcpy(now, head, sizeof now);
	queue<int> q;
	dis[s] = 0, q.ep(s);
	while (!q.empty()) {
		int u = q.front(); q.pop();
		for (int i = head[u]; i; i = e[i].nxt) {
			int v = e[i].to, w = e[i].flow;
			if (dis[v] != inf || !w) continue;
			dis[v] = dis[u] + 1;
			q.ep(v);
		}
	}
	return dis[t] != inf;
}
int dfs(int u, int sum) {
	if (u == t) return sum;
	int res = 0;
	for (int i = now[u]; i && sum; i = e[i].nxt) {
		int v = e[i].to, w = e[i].flow;
		if (dis[v] != dis[u] + 1 || !w) continue;
		int k = dfs(v, min(sum, w));
		e[i].flow -= k, e[i ^ 1].flow += k;
		sum -= k, res += k;
		if (!k) dis[v] = inf;
	}
	return res;
}
pii p[5005];
struct SGT {
	int ls[200005], rs[200005];
	void update(int l, int r, int pos, int u) {
		if (l == r) return addedge(u, t, 1);
		int mid = (l + r) >> 1;
		if (mid >= pos) {
			if (!ls[u]) addedge(u, ls[u] = ++cnt, inf);
			update(l, mid, pos, ls[u]);
		} else {
			if (!rs[u]) addedge(u, rs[u] = ++cnt, inf);
			update(mid + 1, r, pos, rs[u]);
		}
	}
	void query(int l, int r, int L, int R, int v, int u) {
		if (!u) return ;
		if (L <= l && r <= R) return addedge(v, u, 1);
		int mid = (l + r) >> 1;
		if (mid >= L) query(l, mid, L, R, v, ls[u]);
		if (mid < R) query(mid + 1, r, L, R, v, rs[u]);
	}
} sgt;

signed main() {
	n = read();
	rep(i, 1, n) p[i].fi = read(), p[i].se = read();
	s = 1, t = s + 1, rt = t + 1, cnt = rt + 1;
	sort(p + 1, p + n + 1);
	rep(i, 1, n) {
		addedge(s, ++cnt, 1);
		sgt.query(1, n + n, p[i].fi + 1, p[i].se - 1, cnt, rt);
		sgt.update(1, n + n, p[i].se, rt);
	}
	int ans = n + n;
	while (bfs()) ans -= dfs(s, inf);
	printf("%d\n", ans);
	return 0;
}