#include<bits/stdc++.h>

using namespace std;

#define N 100005

int n,l[N];

vector<int>f[N];

int main(){
	int u,v;
	scanf("%d",&n);
	for(int i=1;i<=n;++i){
		scanf("%d%d",&u,&v);
		l[v]=u;
	}
	f[0].push_back(0);
	for(int i=1,j;i<=n+n;++i){
		f[i]=f[i-1];
		f[i][0]=i;
		if(!l[i])continue;
		for(j=f[i].size()-1;~j;--j){
			if(f[i-1][j]>l[i]){
				break;
			}
		}
		if(f[i].size()==j+1){
			f[i].push_back(l[i]);
		}else{
			f[i][j+1]=l[i];
		}
		for(int k=1;k<f[l[i]-1].size();++k){
			if(k+j+1==f[i].size()){
				f[i].push_back(f[l[i]-1][k]);
			}else{
				f[i][k+j+1]=max(f[i][k+j+1],f[l[i]-1][k]);
			}
		}
	}
	printf("%d",f[n+n].size());
	return 0;
}