#include <bits/stdc++.h>

using namespace std;

int cb(vector<pair<int, int>> &v, int l, int r, int x) {
	int ans = -1;
	while (l <= r) {
		int m = (l + r) / 2;
		if (v[m].second <= x) {
			ans = m;
			l = m + 1;
		} else {
			r = m - 1;
		}
	}
	return ans;
}

bool cmp(pair<int, int> a, pair<int, int> b) {
	return a.second < b.second;
}

int main()
{
	ifstream f("heavymetal.in");
	ofstream g("heavymetal.out");
	int n;
	f >> n;
	vector<pair<int, int>> v(n + 1, make_pair(-1, -1));
	vector<int> dp(n + 1, 0);
	for (int i = 1;  i <= n; i++) {
		f >> v[i].first >> v[i].second;
	}
	sort(v.begin(), v.end());
	
	for (int i = 1; i <= n; i++) {
		int p = cb(v, 0, n, v[i].first);
		dp[i] = max(dp[i - 1], v[i].second - v[i].first + dp[p]);
		
	}

	g << dp[n];
}