#include <bits/stdc++.h>
#define rep(i,j,k) for(int i=(j);i<=(k);i++)
#define per(i,j,k) for(int i=(j);i>=(k);i--)
#define uint unsigned int
#define ll long long
#define ull unsigned long long
#define db double
#define ldb long double
#define pii pair<int,int>
#define pll pair<ll,ll>
#define mkp make_pair
#define eb emplace_back
#define SZ(S) (int)S.size()
//#define mod 998244353
//#define mod 1000000007
#define inf 0x3f3f3f3f
#define linf 0x3f3f3f3f3f3f3f3f
using namespace std;

template <class T>
void chkmax(T &x,T y){
	if(x < y) x = y;
}

template <class T>
void chkmin(T &x,T y){
	if(x > y) x = y;
}

inline int popcnt(int x){
	return __builtin_popcount(x);
}

inline int ctz(int x){
	return __builtin_ctz(x);
}


/*ll power(ll p,int k = mod - 2){
	ll ans = 1;
	while(k){
		if(k % 2 == 1) ans = ans * p % mod;
		p = p * p % mod;
		k /= 2;	
	}
	return ans;
}*/
int T,n;
int a[5005],b[5005];

bitset <5005> G[2][5005],okl,okr,cur;
int prv[10005],ans[2][5005],p;
queue <int> Q;
void psh(int u,int v){
	prv[u] = v;
	if(u <= n){
		assert(okl.test(u));
		okl.reset(u);
	}else{
		assert(okr.test(u - n));
		okr.reset(u - n);
		if(!ans[1][u - n]) p = u - n;
	}
	Q.push(u);
}

void bfs(){
	okl.reset();
	okr.reset();
	rep(u,1,n){
		okl.set(u);
		okr.set(u);
	}
	while(!Q.empty()) Q.pop();
	rep(u,1,n) if(!ans[0][u]) psh(u,0);
	p = 0;

	while(!Q.empty()){
		int u = Q.front();
		Q.pop();
		if(u <= n){
			cur = G[0][u] & okr;
			while(cur.any()){
				int v = cur._Find_first();
				psh(v + n,u);
				cur.reset(v);
				if(p) break;
			}
		}else{
			cur = G[1][u - n] & okl;
			while(cur.any()){
				int v = cur._Find_first();
				psh(v,u);
				cur.reset(v);
				if(p) break;
			}
		}
	}
}

int _p[15],tag[25];
int brute(){
	rep(i,1,n) _p[i] = i;
	int result = 0,ssum;
	do{
		fill(tag,tag + 2 * n + 1,0);
		rep(_i,1,n){
			int i = _p[_i]; 
			rep(k,a[i],b[i]) tag[k] = 0;
			tag[a[i]] = tag[b[i]] = 1;
		}
		ssum = 0;
		rep(i,1,2 * n) ssum += tag[i];
		chkmax(result,ssum);
	}while(next_permutation(_p + 1,_p + n + 1));
//	printf("result=%d\n",result);
	return result;
}

void solve(int testid){
	scanf("%d",&n);	
	rep(i,1,n){
		G[0][i].reset();
		G[1][i].reset();
		ans[0][i] = ans[1][i] = 0;
	}
	rep(i,1,n) scanf("%d%d",&a[i],&b[i]);
	rep(i,1,n){
		rep(j,1,n){
			if(a[j] < a[i] && a[i] < b[j] && b[j] < b[i]){
				G[0][i].set(j);
//				printf("%d->%d\n",i,j);
			}
		}
	}

	int answer = 2 * n;
	while(1){
		bfs();
		if(!p) break;
		ans[1][p] = 1;
		p += n;
		int op = 1;
		while(prv[p]){
			if(op){
				G[1][p - n].set(prv[p]);
				G[0][prv[p]].reset(p - n);
			}else{
				G[0][p].set(prv[p] - n);
				G[1][prv[p] - n].reset(p);
			}
//			printf("op=%d p=%d\n",op,p);
			p = prv[p];
			op ^= 1;
		}
		assert(!ans[0][p]);
		ans[0][p] = 1;
		answer--;
//		printf("op=%d p=%d fin\n",op,p);
	}
/*	int answer2 = brute();
	if(answer != answer2){
		cerr << "output=" << answer << " answer=" << answer2 << endl;
		cerr << n << endl;
		rep(i,1,n) cerr << a[i] << " " << b[i] << endl;
	}
	assert(answer == answer2);*/
	printf("%d\n",answer);	
}

int main(){	
//	freopen("test.in","r",stdin);
//	scanf("%d",&T);
	T = 1;
	rep(i,1,T) solve(i);
	return 0;
}