#include<bits/stdc++.h>
#define fr(i,j,k) for(register int i=j;i<=k;++i)
#define rf(i,j,k) for(register int i=j;i>=k;--i)
#define foredge(i,j) for(register int i=head[j];i;i=e[i].nxt)
#define randfind(l,r) (rnd()%((r)-(l)+1)+(l))
#define pb push_back
#define Times printf("Time:%.3lf\n",clock()/CLOCKS_PER_SEC)
using namespace std;
inline int read(){
	int x=0;
	bool f=0;
	char c=getchar();
	while(!isdigit(c)) f|=(c=='-'),c=getchar();
	while(isdigit(c)) x=(x<<3)+(x<<1)+(c^48),c=getchar();
	return f?-x:x;
}
inline void write(int x){
    if(x<0){putchar('-');x=-x;}
    if(x>9)write(x/10);
    putchar(x%10+'0');
}
inline void writeln(int x){write(x); puts("");}
inline void writepl(int x){write(x); putchar(' ');}
//inline void init(){
//	int t=read();
//	while(t--) work();
//}
mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());
const int Maxn=5e3+10;
bitset<Maxn> vc[Maxn];
int n,l[Maxn],r[Maxn];
int ans;
inline void init(){
    n=read();
    fr(i,1,n) l[i]=read(),r[i]=read();
}
int a[Maxn],b[Maxn];
bitset<Maxn> vis;
int mat[Maxn];
inline int bfs(int x){
    queue<int> q;
    int lst,fir=x;
    vis.reset();
    q.push(x);
    lst=-1;
    while(!q.empty() && lst==-1){
        int tp=q.front();q.pop();
        // cout<<"*"<<x<<' '<<tp<<endl;
        auto tmp=(vc[tp]&(~vis));
        for(int y=tmp._Find_first();y<=n;y=tmp._Find_next(y)){
            // cerr<<y<<endl;
            if(vis[y]) continue;vis[y]=1;
            if(!mat[y]){mat[y]=tp;lst=tp;break;}
            int tot=mat[y];
            a[tot]=tp,b[tot]=y,q.push(y);
        }
    }
    if(lst==-1) return 0;
    // cout<<lst<<endl;
    // fr(i,1,n) cout<<a[i]<<' '<<b[i]<<endl;
    for(int i=lst;i!=fir;i=a[i]){
        mat[b[i]]=a[i];
        // cout<<i<<endl;
    }
    return 1;
}
inline void work(){
    ans=2*n;
    fr(i,1,n) fr(j,1,n){
        if(i==j) continue;
        if(l[i]<l[j] && l[j]<r[i] && r[i]<r[j]){
            vc[i][j]=1;
            // cout<<i<<' '<<j<<endl;
        }
    }
    fr(i,1,n) if(bfs(i)) --ans;
    writeln(ans);
}
signed main(){
	// freopen("input.in","r",stdin);
	// freopen("output.out","w",stdout);
    init();work();
    // printf("\nTIME:%.3lf",(double)clock()/CLOCKS_PER_SEC);
	return 0;
}