/*
 * paint_sjz.cpp
 *
 *  Created on: Oct 9, 2016
 *      Author: Steven Zeil
 */

#include <iostream>
#include <fstream>
#include <algorithm>

using namespace std;

struct Interval {
	long start;
	long stop;
	long bestSoFar;

	Interval() : start(0), stop(0), bestSoFar(0)
	{}

	Interval(long strt, long stp)
	: start(strt), stop(stp), bestSoFar(0)
		{}

	bool operator< (const Interval& intrv) const;
	bool operator== (const Interval& intrv) const;

};

bool Interval::operator< (const Interval& intrv) const
{
	if (stop != intrv.stop)
		return stop < intrv.stop;
	else
		return start < intrv.start;
}

bool Interval::operator== (const Interval& intrv) const
{
	return (stop == intrv.stop) && (start == intrv.start);
}

ostream& operator<< (ostream& out, const Interval iv)
{
	out << iv.start << ".." << iv.stop << ":" << iv.bestSoFar;
	return out;
}


void solve (Interval* interval, int k)
{
	sort (interval, interval+k);
	interval[0].bestSoFar = interval[0].stop - interval[0].start;
	for (int i = 1; i <= k; ++i)
	{
		// Option 1 - do not use this interval
		long best1 = interval[i].bestSoFar = interval[i-1].bestSoFar;

		// Option 2. Use this interval with the best combination of intervals
		// up to the start of this one.
		Interval searchKey (interval[i].start, interval[i].start);
		Interval* earlierCase = lower_bound(interval, interval+i, searchKey);
		if (earlierCase != interval) {
			--earlierCase;
		}
		//cerr << "Looking back to " << *earlierCase << endl;
		long best2 = earlierCase->bestSoFar + interval[i].stop - interval[i].start;

		interval[i].bestSoFar = max(best1, best2);
		//cerr << i << " " << interval[i] << ": " << best1 << " " << best2 << endl;
 	}
	cout << interval[k].bestSoFar << endl;
}

void solve (istream& in)
{
    int k;
    in >> k;
    Interval* interval = new Interval[k+1];
    interval[0] = Interval(0,0);
    for (int i = 0; i < k; ++i)
    {
    	long x0, x1;
    	in >> x0 >> x1;
    	interval[i+1] = Interval(x0, x1);
    }
    solve (interval, k);
    delete [] interval;
}


int main (int argc, char** argv)
{
	if (argc > 1)
	{
		for (int i = 1; i < argc; ++i)
		{
			ifstream in(argv[i]);
			solve (in);
		}
	}
	else
	{
		solve (cin);
	}
}