#include<iostream>
#include<algorithm>
using namespace std;
struct grass{
	int x,y;
}g[150001];
int n,f[150001];
bool cmp(grass a,grass b){
	return a.y<b.y;
}
int main(){
	cin>>n;
	for(int i=1;i<=n;i++) cin>>g[i].x>>g[i].y;
	sort(g+1,g+n+1,cmp);
	for(int i=1;i<=n;i++){
		f[i]=g[i].y-g[i].x+1;
		for(int j=1;j<i;j++){
			if(g[j].y<g[i].x) f[i]=max(f[i],f[j]+(g[i].y-g[i].x+1));
			else f[i]=max(f[i],f[j]);
		}
	}
	cout<<f[n];
}