#include <iostream>
#include <fstream>
#include <algorithm>
#define f first
#define s second

using namespace std;
ifstream fin("heavymetal.in");
ofstream fout("heavymetal.out");
int n,i,ok,st,dr,mid;
int d[100002];
pair<int,int> v[100002];

int main()
{
    fin>>n;
    for(i=1;i<=n;i++)
        fin>>v[i].s>>v[i].f;
    sort(v+1, v+n+1);
    d[1]=v[1].f-v[1].s;
    for(i=2;i<=n;i++)
    {
        ok=v[i].s;
        st=1;dr=i-1;
        while(st<=dr)
        {
            mid=(st+dr)/2;
            if(v[mid].f<=ok)
                st=mid+1;
            else
                dr=mid-1;
        }
        d[i]=max(v[i].f-v[i].s+d[dr], d[i-1]);
    }
    fout<<d[n];
    fin.close();
    fout.close();
    return 0;
}