Infinite Inversions

题意翻译

现在有一个由所有正整数组成的无限递增序列： $p = {1,2,3,...}$ 。 对这个序列执行 $n$ 次交换操作。每次一个操作，给出两个整数 $a,b$ ，交换位置 $a$ 和 $b$ 处的元素。 你的任务是在所有操作结束后，输出最终序列的逆序对个数，即满足 $i < j$ 且 $p_i > p_j$ 的有序数对 $(i,j)$ 的数量。

题目描述

There is an infinite sequence consisting of all positive integers in the increasing order: $ p={1,2,3,...} $ . We performed $ n $ swap operations with this sequence. A $ swap(a,b) $ is an operation of swapping the elements of the sequence on positions $ a $ and $ b $ . Your task is to find the number of inversions in the resulting sequence, i.e. the number of such index pairs $ (i,j) $ , that $ i&lt;j $ and $ p_{i}&gt;p_{j} $ .

输入输出格式

输入格式

The first line contains a single integer $ n $ ( $ 1<=n<=10^{5} $ ) — the number of swap operations applied to the sequence. Each of the next $ n $ lines contains two integers $ a_{i} $ and $ b_{i} $ ( $ 1<=a_{i},b_{i}<=10^{9} $ , $ a_{i}≠b_{i} $ ) — the arguments of the swap operation.

输出格式

Print a single integer — the number of inversions in the resulting sequence.

输入输出样例

输入样例 #1

2
4 2
1 4

输出样例 #1

4

输入样例 #2

3
1 6
3 4
2 5

输出样例 #2

15

说明

In the first sample the sequence is being modified as follows: . It has 4 inversions formed by index pairs $ (1,4) $ , $ (2,3) $ , $ (2,4) $ and $ (3,4) $ .