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#include<iostream>
#include<string>
#include<map>
#include<algorithm>
#define int long long
using namespace std;
int n;
int m[20005], k[20005];
int endn = 0;
int beginn = 0;
int ans = 0;
signed main()
{
	cin >> n;
	for (int i = 0; i < n; i++)
	{
		cin >> m[i] >> k[i];
	}
	sort(m, m + n);
	sort(k, k + n);
	beginn = m[0];
	endn = k[0];
	for (int i = 0; i < n; i++)
	{

		if (k[i] > m[i + 1] && i != n - 1)
		{
			endn = k[i + 1];
		}
		else
		{
			ans += endn - beginn;
			beginn = m[i + 1];
			endn = k[i + 1];
		}
	}
	cout << ans;
	return 0;
}