#include<bits/stdc++.h>
#define rep(i, n) for(int i = 0; i < n; ++i)
using namespace std;
typedef long long ll;
typedef vector<int> vi;
const int inf = 0x3f3f3f3f;

int n;
array<int, 2> a[5050];

int cn = 0;
namespace mf{
	int hd[250250], cur[250250], dis[250250];
	int to[250250], cap[250250], nxt[250250], ce = 0;
	void clr(){
		memset(hd, -1, sizeof(hd));
	}
	void ae(int f, int t, int c){
		//cout << "ae " << f << " " << t << " " << c << endl;
		nxt[ce] = hd[f], to[ce] = t, cap[ce] = c, hd[f] = ce++;
		nxt[ce] = hd[t], to[ce] = f, cap[ce] = 0, hd[t] = ce++;
	}
	bool bfs(int S, int T){
		fill(dis, dis+cn, inf);
		static int q[250250];
		int qhd = 0, qrr = 0;
		q[qrr++] = S, dis[S] = 0;
		while(qhd < qrr){
			int u = q[qhd++];
			for(int e = hd[u]; e >= 0; e = nxt[e]){
				if(!cap[e]) continue;
				int t = to[e];
				if(dis[t] > dis[u] + 1){
					dis[t] = dis[u] + 1;
					q[qrr++] = t;
				}
			}
		}
		return dis[T] < inf;
	}
	int dfs(int u, int dest, int f){
		if(u == dest) return f;
		int nf = 0;
		for(int &e = cur[u]; e >= 0; e = nxt[e]){
			int t = to[e];
			if(!cap[e] || dis[t] != dis[u] + 1) continue;
			int ret = dfs(t, dest, min(f, cap[e]));
			nf += ret, cap[e] -= ret, cap[e^1] += ret;
			if(nf == f) break;
		}
		return nf;
	}
	int mf(int S, int T){
		int ret = 0;
		while(bfs(S, T)){
			rep(i, cn) cur[i] = hd[i];
			ret += dfs(S, T, inf);
		}
		return ret;
	}
}

int nid[40040];
int upd(int p, int l, int r, int u){
	nid[u] = cn++;
	//cout << "upd " << p << " " << l << " " << r << " " << u << ": " << nid[u] << endl;
	if(l == r)
		return nid[u];
	int mid = (l+r) >> 1, ret;
	if(p <= mid){
		ret = upd(p, l, mid, u+u);
	} else {
		ret = upd(p, mid+1, r, u+u+1);
	}
	if(nid[u+u] >= 0) mf::ae(nid[u], nid[u+u], inf);
	if(nid[u+u+1] >= 0) mf::ae(nid[u], nid[u+u+1], inf);
	return ret;
}
void segae(int f, int tl, int tr, int l, int r, int u){
	//cout << "segae " << f << " " << tl << " " << tr << " " << l << " " << r << " " << u << ": " << nid[u] << endl;
	if(nid[u] < 0 || tl > r || l > tr) return ;
	if(tl <= l && r <= tr) return mf::ae(f, nid[u], 1);
	int mid = (l+r) >> 1;
	segae(f, tl, tr, l, mid, u+u), segae(f, tl, tr, mid+1, r, u+u+1);
}

int main(){
	freopen("frog.in", "r", stdin);
	freopen("frog.out", "w", stdout);
	ios::sync_with_stdio(false);

	cin >> n;
	rep(i, n)
		cin >> a[i][0] >> a[i][1], --a[i][0], --a[i][1];
	sort(a, a+n);
	
	memset(nid, -1, sizeof(nid));
	mf::clr();
	cn = 2;
	rep(i, n){
		//cout << "-----------" << i << ": " << a[i][0] << " " << a[i][1] << "-----------------" << endl;
		mf::ae(upd(a[i][1], 0, 2*n-1, 1), 1, 1);
		mf::ae(0, cn, 1);
		segae(cn, a[i][0]+1, a[i][1]-1, 0, 2*n-1, 1);
		++cn;
	}

	cout << 2*n - mf::mf(0, 1) << "\n";

	return 0;
}

// by zxb
// start coding at 15:32
// submission #1 at 16:14