#include<bits/stdc++.h>
using namespace std;
const int N=1e6+10;
template<typename T>void qr(T& x)
{
	x=0;int f=1;char c=getchar();
	for( ;!isdigit(c);c=getchar())if(c=='-')f=-1;
	for( ; isdigit(c);c=getchar())x=x*10+c-48;
	x=x*f;
}
struct node{int x,y,L;}a[N];
int n,f[N];
int find(int x)
{
	int L=1,R=n,mid,ans=0;
	while(L<=R)
	{
		mid=(L+R)>>1; 
		if(a[mid].y<=x)L=mid+1,ans=mid;
		else R=mid-1;
	}
	return ans;
}
int main()
{
    qr(n);
    for(int i=1;i<=n;i++)
    {
        qr(a[i].x);qr(a[i].y);
		a[i].L=a[i].y-a[i].x;
    }
    sort(a+1,a+n+1,[](const node &n1,const node &n2){return n1.y<n2.y;});
    memset(f,0,sizeof(f));
    a[0]={0,0};
	int ans=0;
    for(int i=1;i<=n;i++)
    {
    	f[i]=f[i-1];
    	int j=find(a[i].x);
        f[i]=max(f[i],f[j]+a[i].L);
        ans=max(ans,f[i]);
    }
    printf("%d\n",ans);
    return 0;
}