#include<bits/stdc++.h>
#define Gc() getchar() 
#define Me(x,y) memset(x,y,sizeof(x))
#define Mc(x,y) memcpy(x,y,sizeof(x))
#define d(x,y) ((m)*(x-1)+(y))
#define R(n) (rnd()%(n)+1)
#define Pc(x) putchar(x)
#define LB lower_bound
#define UB upper_bound
#define fi first
#define se second
using namespace std;using ll=long long;using db=double;using lb=long db;using ui=unsigned;using ull=unsigned long long;using pii=pair<int,int>;using LL=__int128;
const int N=5e3+5,M=N*40+5,K=(1<<25)+5,mod=998244353,Mod=mod-1;const db eps=1e-9;const ll INF=1e18+7;mt19937 rnd(time(0));
int n,L[N],R[N];
bitset<N> A[N],vis;int mch[N];
int dfs(int x){
	vis[x]=1;
	for(int i=1;i<=n;i++) if(A[x][i]&&!vis[i]) {
		if(!mch[i]||dfs(mch[i])) {mch[i]=x;return 1;}
	}
	return 0;
}
void Solve(){
	int i,j;scanf("%d",&n);
	for(i=1;i<=n;i++) scanf("%d%d",&L[i],&R[i]);
	for(i=1;i<=n;i++){
		for(j=1;j<=n;j++) if(i^j&&L[j]<=L[i]&&L[i]<=R[j]&&R[j]<=R[i]) A[i][j]=1;
	}
	int Ct=2*n;
	for(i=1;i<=n;i++) if(vis.reset(),dfs(i)) Ct--;
	printf("%d\n",Ct);
}
int main(){
	int t;
	// scanf("%d",&t);
	t=1;
	while(t--) Solve();
	cerr<<clock()*1.0/CLOCKS_PER_SEC<<'\n';
}