#include <fstream>
#include <algorithm>
#include <utility>

using namespace std;

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

int n;
pair<int, int> v[100001];
int in[100001], t[100001];

bool cmp(int i1, int i2)
{
	if (v[i1].second != v[i2].second)
		return v[i1].second < v[i2].second;
	else
		return v[i1].first <= v[i2].first;
}

int main()
{
	fin >> n;
	for (int i = 1; i <= n; ++i)
	{
		fin >> v[i].first >> v[i].second;
		in[i] = i;
	}
	sort(in + 1, in + n + 1, cmp);

	int now, step;

	for (int i = 1; i <= n; ++i)
	{
		for (step = 1; (step << 1) < i; step <<= 1);
		for (now = 0; step; step >>= 1)
			if (now + step < i && v[in[now + step]].second <= v[in[i]].first)
				now += step;
		t[in[i]] = max(t[in[i - 1]], t[in[now]] + v[in[i]].second - v[in[i]].first);
	}

	fout << t[in[n]];

	fin.close();
	fout.close();
}