#include <fstream>
#include <algorithm>

using namespace std;
ifstream fin("heavymetal.in");
ofstream fout("heavymetal.out");
struct kys{int x,y;}a[100001];
int compare (kys a,kys b)
{
    return a.y<b.y||a.y==b.y&&a.x<b.x;
}
int n,i,max1,s[100001],j,st,dr,mid;
int main()
{
    fin>>n;
    for(i=1;i<=n;i++)
    {
        fin>>a[i].x>>a[i].y;
    }
    sort(a+1,a+n+1,compare);
    for(i=1;i<=n-1;i++)
    {
        st=i+1;
        dr=n;
        while(st<=dr)
        {
            mid=(st+dr)/2;
            if(a[mid].x>=a[i].y)
            {
                st=mid+1;
            }
            else dr=mid-1;
        }
        for(j=mid;j<=n;j++)
        {
            if(s[j]<s[i]+a[i].y-a[i].x) s[j]=s[i]+a[i].y-a[i].x;
            else break;
        }
    }
    for(i=1;i<=n;i++)
    {
        s[i]+=(a[i].y-a[i].x);
        if(s[i]>max1) max1=s[i];
    }
    fout<<max1;
    return 0;
}