A9958. Infinite Inversions

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 $i<j$ and $p_{i}>p_{j}$ .

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.

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

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 $(3,4)$ .