$题目$

#include<bits/stdc++.h>
using namespace std;
int main()
{
    long long j,n,m,high=0,sum=0;
    cin>>j;
    for(int i=1;i<=j;i++)
    {
        cin>>n>>m;
        sum=m-n;
    }
    if(sum>high)
    {
       	high=sum;
       	cout<<high;
	}
    else if(sum<=high)
    	cout<<"vacant";
    return 0;
}