#include<stdio.h>
#include<algorithm>
#include<map>
#define NMAX 100001
using namespace std;
FILE *f=fopen("heavymetal.in","r");
FILE *g=fopen("heavymetal.out","w");
struct timp{
	int a;
	int b;
} v[NMAX];
int ind[NMAX],sol[NMAX],N;
int cmp(const int &x,const int &y){
	return v[x].b < v[y].b;	
}
map <int,int> t;
int s(int x){
	while(t[x] ==0 )
		x--;
return x;	
}
int main(){
	fscanf(f,"%d",&N);
	for(int i=1;i<=N;++i){
		fscanf(f,"%d%d",&v[i].a,&v[i].b);
		ind[i]=i;}
	sort(ind+1,ind+N+1,cmp);
	t[0]=0;
	sol[1]=v[ind[1]].b-v[ind[1]].a;
	for(int i=1;i<=N;++i)
		if( t[v[ind[i]].b] == 0)
			t[v[ind[i]].b] = i;
	for(int i=2;i<=N;++i)
		sol[i]=max(sol[i-1],v[ind[i]].b-v[ind[i]].a+sol[t[s(v[ind[i]].a)]]);!
	fprintf(g,"%d",sol[N]);
return 0;
}