#pragma GCC optimize(3,"Ofast","inline")
#include <bits/stdc++.h>
using namespace std;
#define int long long
inline int read()
{
	char ch=getchar();
	int x=0,m=1;
	while(!isdigit(ch)){
		if (ch=='-') m=-1;
		ch=getchar();
	}
	while(isdigit(ch)){
		x=x*10+ch-'0';
		ch=getchar();
	}
	return x*m;
}
inline void write(int x)
{
	if (x<0) putchar('-'),x=-x;
	if (x>=10) write(x/10);
	putchar(x%10+'0');
}
int n,w[1010];
struct Node{
	int l,w;
}a[1010];
inline bool cmp(Node x,Node y)
{
	return x.l < y.l || ( x.l == y.l && x.w < y.w );
}
signed main()
{
	n=read();
	for (int i=1;i<=n;i++) a[i].l=read(),a[i].w=read();
	sort(a+1,a+1+n,cmp);
	int k=1;
	w[1]=a[1].w;
	for (int i=2;i<=n;i++){
		int p=0;
		for (int j=1;j<=k;j++){
			if (w[j]<=a[i].w){
				if (!p) p=j;
				else if (w[j]>=w[p]) p=j;
			}
		}
		if (!p) w[++k]=a[i].w;
		else w[p]=a[i].w;
	}
	write(k);
	return 0;
}

自行参考