#pragma GCC optimize(2)
#pragma GCC optimize(3)
#pragma GCC target("avx")
#pragma GCC optimize ("O2")
#pragma GCC optimize ("O3")
#pragma GCC optimize ("O1")
#pragma GCC optimize ("O0")
#pragma GCC optimize ("Ofast")
#pragma GCC optimize("-fdelete-null-pointer-checks,inline-functions-called-once,-funsafe-loop-optimizations,-fexpensive-optimizations,-foptimize-sibling-calls,-ftree-switch-conversion,-finline-small-functions,inline-small-functions,-frerun-cse-after-loop,-fhoist-adjacent-loads,-findirect-inlining,-freorder-functions,no-stack-protector,-fpartial-inlining,-fsched-interblock,-fcse-follow-jumps,-fcse-skip-blocks,-falign-functions,-fstrict-overflow,-fstrict-aliasing,-fschedule-insns2,-ftree-tail-merge,inline-functions,-fschedule-insns,-freorder-blocks,-fwhole-program,-funroll-loops,-fthread-jumps,-fcrossjumping,-fcaller-saves,-fdevirtualize,-falign-labels,-falign-loops,-falign-jumps,unroll-loops,-fsched-spec,-ffast-math,Ofast,inline,-fgcse,-fgcse-lm,-fipa-sra,-ftree-pre,-ftree-vrp,-fpeephole2",3)
#pragma GCC target("avx","sse2")
#pragma GCC optimize("Ofast")
#pragma GCC optimize("inline")
#pragma GCC optimize("-fgcse")
#pragma GCC optimize("-fgcse-lm")
#pragma GCC optimize("-fipa-sra")
#pragma GCC optimize("-ftree-pre")
#pragma GCC optimize("-ftree-vrp")
#pragma GCC optimize("-fpeephole2")
#pragma GCC optimize("-ffast-math")
#pragma GCC optimize("-fsched-spec")
#pragma GCC optimize("unroll-loops")
#pragma GCC optimize("-falign-jumps")
#pragma GCC optimize("-falign-loops")
#pragma GCC optimize("-falign-labels")
#pragma GCC optimize("-fdevirtualize")
#pragma GCC optimize("-fcaller-saves")
#pragma GCC optimize("-fcrossjumping")
#pragma GCC optimize("-fthread-jumps")
#pragma GCC optimize("-funroll-loops")
#pragma GCC optimize("-fwhole-program")
#pragma GCC optimize("-freorder-blocks")
#pragma GCC optimize("-fschedule-insns")
#pragma GCC optimize("inline-functions")
#pragma GCC optimize("-ftree-tail-merge")
#pragma GCC optimize("-fschedule-insns2")
#pragma GCC optimize("-fstrict-aliasing")
#pragma GCC optimize("-fstrict-overflow")
#pragma GCC optimize("-falign-functions")
#pragma GCC optimize("-fcse-skip-blocks")
#pragma GCC optimize("-fcse-follow-jumps")
#pragma GCC optimize("-fsched-interblock")
#pragma GCC optimize("-fpartial-inlining")
#pragma GCC optimize("no-stack-protector")
#pragma GCC optimize("-freorder-functions")
#pragma GCC optimize("-findirect-inlining")
#pragma GCC optimize("-fhoist-adjacent-loads")
#pragma GCC optimize("-frerun-cse-after-loop")
#pragma GCC optimize("inline-small-functions")
#pragma GCC optimize("-finline-small-functions")
#pragma GCC optimize("-ftree-switch-conversion")
#pragma GCC optimize("-foptimize-sibling-calls")
#pragma GCC optimize("-fexpensive-optimizations")
#pragma GCC optimize("-funsafe-loop-optimizations")
#pragma GCC optimize("inline-functions-called-once")
#pragma GCC optimize("-fdelete-null-pointer-checks")
#include <bits/stdc++.h>
#define INF 1000000000
#define LINF 1000000000000000000
#define MOD 1000000007
#define mod 998244353
#define F first
#define S second
#define ll int
#define N 5010
using namespace std;
ll n,col,mat[N*2],vid[N*2];
pair<ll,ll> p[N];
bitset<N> nei[N];
inline bool dfs(ll x)
{
	ll i;
	vid[x]=col;
	for(i=nei[x]._Find_first();i<N;i=nei[x]._Find_next(i))
	{
		if(mat[i+n]==-1)
		{
			mat[x]=i+n,mat[i+n]=x;
			return true;
		}
		if(vid[mat[i+n]]!=col&&dfs(mat[i+n]))
		{
			mat[x]=i+n,mat[i+n]=x;
			return true;
		}
	}
	return false;
}
ll solve()
{
	ll i,ret=0;
	for(i=0;i<n*2;i++)
	{
		mat[i]=-1;
	}
	col=0;
	while(true)
	{
		col++;
		ll cnt=0;
		for(i=0;i<n;i++)
		{
			if(mat[i]==-1&&dfs(i))
			{
				cnt++;
			}
		}
		if(cnt==0)
		{
			break;
		}
		ret+=cnt;
	}
	return ret;
}
int main(){
	ll i;
	scanf("%d",&n);
	for(i=0;i<n;i++)
	{
		scanf("%d%d",&p[i].F,&p[i].S);
	}
	sort(p,p+n);
	set<pair<ll,ll> > alls;
	for(i=0;i<n;i++)
	{
		while(!alls.empty())
		{
			if((*alls.begin()).F>=p[i].F)
			{
				break;
			}
			alls.erase(alls.begin());
		}
		for(set<pair<ll,ll> >::iterator it=alls.begin();it!=alls.end()&&(it->F)<p[i].S;it++)
		{
			nei[i][it->S]=1;
		}
		alls.insert(make_pair(p[i].S,i));
	}
	printf("%d\n",n*2-solve());
	return 0;
}