#include <iostream>
#include <fstream>
#include <algorithm>
#include <cmath>
#define NMAX 100005

using namespace std;

ifstream fin("heavymetal.in");
ofstream fout("heavymetal.out");

struct sp
{
    int x,y;
}v[NMAX];

int x[NMAX],nr,n,rez;

inline int comp(sp a, sp b)
{
    if(a.y<b.y) return 1;
    if(a.y==b.y) return a.x<b.x;
    return 0;
}

inline void citire()
{
    fin>>n;
    for (int i=1;i<=n;i++)
        fin>>v[i].x>>v[i].y;
}

inline int caut(int x)
{
    int l=1,r=n,mid=(l+r)/2;
    while(l<=r)
    {
        mid=(l+r)/2;
        if(v[mid].y<=x) l=mid+1;
        else r=mid-1;
    }
    return r;
}

inline void solve()
{
    int i,j;
    for (i=1;i<=n;i++)
    {
        int aux=caut(v[i].x);
        x[i]=max(x[i-1],x[aux]+v[i].y-v[i].x);
        rez=max(rez,x[i]);
    }
}

int main()
{
    citire();
    sort(v+1,v+n+1,comp);
    solve();
    fout<<rez;
    fin.close();
    fout.close();
    return 0;
}