#include<bits/stdc++.h>
#define fi first
#define se second
#define pb push_back
#define ll long long
using namespace std;
const int N=5005;
int n,tot,l[N],r[N],match[N];
int px[N],py[N];
bitset<N>to[N],vs;
queue<int>Q;
int bfs(int u){
    while(Q.size())Q.pop();
    vs.set(),Q.push(u);int v=-1;
    vs[u]=0;
    while(Q.size()){
        int x=Q.front();Q.pop();
        bitset<N>tmp=vs&to[x];
        for(int y=tmp._Find_first();y<=n;y=tmp._Find_next(y)){
            int z=match[y];vs[y]=0;
            if(z==0){
                match[y]=x,v=x;
                break;
            }
            Q.push(z),px[z]=x,py[z]=y;
        }if(~v)break;
    }if(v==-1)return 0;
    while(v!=u){
        match[py[v]]=px[v];
        v=px[v];
    }
    return 1;
}
int main(){
    //freopen("data.in","r",stdin);
    ios::sync_with_stdio(false);
    cin.tie(0),cout.tie(0);
    cin>>n;
    for(int i=1;i<=n;i++){
        cin>>l[i]>>r[i];
    }
    for(int i=1;i<=n;i++){
        for(int j=1;j<=n;j++){
            if(l[i]<l[j]&&l[j]<r[i]-1&&r[i]-1<r[j]-1){
                to[i][j]=1;
            }
        }
    }
    for(int i=1;i<=n;i++){
        tot+=bfs(i);
    }cout<<2*n-tot;
}