G.Trace
There's a beach in the first quadrant. And from time to time, there are sea waves. A wave ( xx , yy) means the wave is a rectangle whose vertexes are ( 00 , 00 ), ( xx , 00 ), ( 00 , yy ), ( xx , yy ). Every time the wave will wash out the trace of former wave in its range and remain its own trace of ( xx , 00 ) -> ( xx , yy ) and ( 00 , yy ) -> ( xx , yy ). Now the toad on the coast wants to know the total length of trace on the coast after n waves. It's guaranteed that a wave will not cover the other completely.
Input
The first line is the number of waves n(n \le 50000)n(n≤50000).
The next nn lines，each contains two numbers xxyy ,( 0 < x0<x , y \le 10000000y≤10000000 )，the ii-th line means the ii-th second there comes a wave of ( xx , yy ), it's guaranteed that when 1 \le i1≤i , j \le nj≤n，x_i \le x_jxi≤xj and y_i \le y_jyi≤yj don't set up at the same time.
Output
An Integer stands for the answer.
Hint：
As for the sample input, the answer is 3+3+1+1+1+1=103+3+1+1+1+1=10
样例输入
3 1 4 4 1 3 3
样例输出
10
傻逼题，傻逼做不出来的题。。。。。 QAQ
浓缩题意：不断给(0,0)位置覆盖长x宽y的矩形纸片，问最后露出来的边长长度之和是多少（x、y坐标轴不算）
重中之重的一点是：保证没有一个矩形会被完全覆盖，也就是说，有几个矩形，就会露出几个小“尖尖”，如图
那问题就很简单了（但我还是想不到）：
1.从最后一块矩形开始从后向前遍历
2.横边和竖边分别算最后相加
3.对于横边：找到已遍历的边中距离当前边最近的一条（二分查找），给sum加上它们的高度差。竖边同理，给sum加上长度差
AC代码：
