CodeForce-785B Anton and Classes（简单贪心）

Anton and Classes

Anton likes to play chess. Also he likes to do programming. No wonder that he decided to attend chess classes and programming classes.

Anton has n variants when he will attend chess classes, i-th variant is given by a period of time (l_1, i, r_1, i). Also he has m variants when he will attend programming classes, i-th variant is given by a period of time (l_2, i, r_2, i).

Anton needs to choose exactly one of n possible periods of time when he will attend chess classes and exactly one of m possible periods of time when he will attend programming classes. He wants to have a rest between classes, so from all the possible pairs of the periods he wants to choose the one where the distance between the periods is maximal.

The distance between periods (l₁, r₁) and (l₂, r₂) is the minimal possible distance between a point in the first period and a point in the second period, that is the minimal possible |i - j|, where l₁ ≤ i ≤ r₁ and l₂ ≤ j ≤ r₂. In particular, when the periods intersect, the distance between them is 0.

Anton wants to know how much time his rest between the classes will last in the best case. Help Anton and find this number!

Input

The first line of the input contains a single integer n (1 ≤ n ≤ 200 000) — the number of time periods when Anton can attend chess classes.

Each of the following n lines of the input contains two integers l_1, i and r_1, i (1 ≤ l_1, i ≤ r_1, i ≤ 10⁹) — the i-th variant of a period of time when Anton can attend chess classes.

The following line of the input contains a single integer m (1 ≤ m ≤ 200 000) — the number of time periods when Anton can attend programming classes.

Each of the following m lines of the input contains two integers l_2, i and r_2, i (1 ≤ l_2, i ≤ r_2, i ≤ 10⁹) — the i-th variant of a period of time when Anton can attend programming classes.

Output

Output one integer — the maximal possible distance between time periods.

Example

Input

3
1 5
2 6
2 3
2
2 4
6 8

Output

3

Input

3
1 5
2 6
3 7
2
2 4
1 4

Output

0

Note

In the first sample Anton can attend chess classes in the period (2, 3) and attend programming classes in the period (6, 8). It's not hard to see that in this case the distance between the periods will be equal to 3.

In the second sample if he chooses any pair of periods, they will intersect. So the answer is 0.

给两个事件各自能够在哪些时间段去完成;

让你选择两个时间段来完成这两件事情;

要求两段时间的间隔最长(休息的时间最长);

只需要贪心计算即可,如果a事件先b事件后,那么用b的最大开始时间减去a的最小结束时间。

同理,如果b事件先a事件后,那么用a的最大开始时间减去b的最小结束时间。

判断两者谁更大，如果都是负数，则输出0(没有结果)。

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 int main()
 4 {
 5     int n;
 6     cin>>n;
 7     int a1=0,b1=2000000000;
 8     int a2=0,b2=2000000000;
 9     for(int i=0;i<n;i++)
10     {
11         int a,b;
12         cin>>a>>b;
13         if(a>a1) a1=a;
14         if(b<b1) b1=b;
15     }
16     int m;
17     cin>>m;
18     for(int i=0;i<m;i++)
19     {
20         int a,b;
21         cin>>a>>b;
22         if(a>a2) a2=a;
23         if(b<b2) b2=b;
24     }
25     int ans=max(a1-b2,a2-b1);
26     if(ans>0) cout<<ans;
27     else
28     cout<<"0";
29     return 0;
30 }