#include <bits/stdc++.h>
using namespace std;

int main()
{
	int x, y;
	int n, maxl = 0, maxr = 0, len1 = 0, len2 = 0, ans = 0;
	cin >> n;
	for (int i = 1; i <= n; i++)
	{
		cin >> x >> y;
		len1 = max(y, maxl) + max(x - y, maxr);
		len2 = max(x - y, maxl) + max(y, maxr);
		ans = max(ans, max(len1, len2));
		if (ans = len1)
		{
			maxl = max(y, maxl);
			maxr = max(x - y, maxr);
		}
		else if (ans = len2)
		{
			maxl = max(x - y, maxl);
			maxr = max(y, maxr);
		}
	}
	cout << ans << endl;
	return 0;
}