#include <bits/stdc++.h>
using namespace std;
int main()
{
	const int bgx = 8, n = 7;
	int a[10001], sum[10001], t1, t2, s = 0;
	memset(a, 0, sizeof (a));
	memset(sum, 0, sizeof (sum));
	for (int i = 1; i <= n; i++)
	{
		int a1, a2;
		cin >> a1 >> a2;
		t1 = max(a1, a2);
		t2 = min(a1, a2);
		int c = t1 - t2;
		if (c > bgx)
		{
			sum[i] = c;
			s++;
		}
	}
	if (s >= 2)
	{
		for (int i = 1; i <= n; i++)
		{
			if (a[i])
			{
				cout << a[i] << endl;
				return 0;
			}
		}
	}
	int mx = 0;
	for (int i = 1; i <= n; i++)
	{
		mx = max(a[i], mx);
	}
	cout << mx << endl;
	return 0;
}