#include <fstream>
#include <vector>

using namespace std;

ifstream f ("heavymetal.in");
ofstream g ("heavymetal.out");

int n, x, y, t, d[132003];

vector <int> v[132003];

int main()
{
	f >> n;
	for(int i = 1; i <= n; i++)
	{
		f >> x >> y;
		v[y].push_back(x);
		t = max(t, y);
	}
	for(int i = 1; i <= t; i++)
	{
		d[i] = d[i - 1];
		for(int j = 0; j < v[i].size(); j++) 
			d[i] = max(d[i], d[v[i][j]] + i - v[i][j]);
	}
	g << d[t];
}