#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>
#include <queue>
#include <cmath>
#include <stack>
#include <cstring>

using namespace std;

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

const int DIM = 100005;

long long DP[DIM],n,sol,Max[DIM];

struct Point
{
    int x,y;
}P[DIM];

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

bool Compare(Point a, Point b)
{
    return a.y<b.y;
}

int Search(int value)
{
    int st=1,dr=n,ans=0;
    while(st<=dr)
        {
            int mij=(st+dr)/2;
            if(P[mij].y<=value)
                {
                    ans=max(ans,mij);
                    st=mij+1;
                }
            else
                dr=mij-1;
        }
    return ans;
}

void Solve()
{
    for(int i=1;i<=n;i++)
        {
            DP[i]=P[i].y-P[i].x;
            Max[i]=max(Max[i-1],DP[i]);
        }
    for(int i=2;i<=n;i++)
        {
            int Find=P[i].x;
            sol=Search(Find);
            DP[i]+=Max[sol];
            Max[i]=max(Max[i-1],DP[i]);
        }
}

void Print()
{
    fout<<Max[n]<<'\n';
}

int main()
{
    Read();
    sort(P+1,P+1+n,Compare);
    Solve();
    Print();
}