#pragma GCC optimize("Ofast,unroll-loops")
#include <bits/stdc++.h>
using namespace std;
bool a[5005][5005];
int vis[5005],mch[5005],l[5005],r[5005],n;
int match(int x){
    for(int i=1;i<=n;i++)
        if(a[x][i]&&!vis[i]){
            vis[i]=1;
            if(!mch[i]||match(mch[i])){
                mch[i]=x;
                return 1;
            }
        }
    return 0;
}
int main() {
    int T = 1, kase = 0;
    //cin >> T;
    while (T--) {
        cin>>n;
        for(int i=1;i<=n;i++) cin>>l[i]>>r[i];
        for(int i=1;i<=n;i++)
            for(int j=i+1;j<=n;j++){
                if(l[i]<l[j]&&r[i]<r[j]&&r[i]>l[j]) a[j][i]=1;
                else if(l[j]<l[i]&&r[j]<r[i]&&r[j]>l[i]) a[i][j]=1;
            }
        for(int i=1;i<=n;i++){
            memset(vis,0,sizeof(vis));
            match(i);
        }
        int ans=n*2;
        for(int i=1;i<=n;i++) if(mch[i]) ans--;
        printf("%d\n",ans);
    }
    return 0;
}