#include<bits/stdc++.h>
using namespace std;
#define ll int
#define f(i,a,b) for(ll i=a;i<=b;i++)
inline ll rd(){
    ll x=0,f=1;char c=getchar();
    while(!isdigit(c)){if(c=='-')f=-1;c=getchar();}
    while(isdigit(c))x=x*10+c-'0',c=getchar();
    return x*f;
}
#define d rd()
ll n,m;
ll l[5010],r[5010];
bitset<10010>vis;
ll ma[10010];
vector<ll>e[10010];
ll res;
bool dfs(ll u){
    for(int i=0;i<e[u].size();i++){
        ll v=e[u][i];
		if(!vis[v]){vis[v]=1;
			if(!ma[v]||dfs(ma[v])){
				ma[v]=u;return 1;
			}
		}
    }return 0;
}bool fl[10010];
int main(){
    n=d;f(i,1,n)l[i]=d,r[i]=d,fl[r[i]]=1;
    f(i,1,n)f(j,i+1,n)if(l[i]<l[j]&&l[j]<r[i]&&r[i]<r[j])e[r[i]].push_back(l[j]);
    
    f(i,1,n*2)if(fl[i])vis.reset(),res+=dfs(i);
    cout<<2*n-res;
    return 0;
}
/*
5
2 3
6 7
1 9
5 10
4 8
*/