求助，80pts

#include <iostream>
using namespace std;

int a[100010], b[100010], maxn, maxid;
bool flag;

int main() 
{
	int n;
	cin >> n;
	for(int i = 1; i <= n; i++)
	{
		cin >> a[i] >> b[i];
		if(b[i] > a[i] - b[i])b[i] = a[i] - b[i];
		if(a[i] - b[i] > maxn)
		{
			maxn = a[i] - b[i];
			maxid = i;
		}
	}
    for(int i = 1; i <= n; i++)
    {
        if(maxn <= a[i] && i != maxid && a[maxid] <= a[i])flag = true;
    }
    if(flag == false)
	{
		cout << a[maxid] << endl;
		return 0;
	}
	int ans = 0;
	for(int i = 1; i <= n; i++)
	{
		if(i != maxid)ans = max(maxn + a[i] - b[i], ans);
	}
	cout << ans << endl;
	return 0;
}