#include <bits/stdc++.h> 
using namespace std;
int a[5005], b[5005];
int main()
{
	int n, sum = 0, t;
	cin >> n;
	for (int i = 1; i <= n; ++i) 
	{
    	cin >> a[i] >> b[i];
	}
	for (int i = 1; i <= n - 1; ++i) 
	{
    	t = a[i + 1] - a[i];
    	if (b[i] >= t) 
		{
			continue;
		}
		if(sum > (t - b[i]))
		{
			sum = sum;
		}
		else
		{
			sum = t - b[i];
		} 
	}
	cout << sum;
	return 0;
 }