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 .

输入描述:

The first line contains a single integer n (1 ≤ n ≤ 105) — the number of swap operations applied to the sequence.Each of the next n lines contains two integers ai and bi (1 ≤ ai, bi ≤ 109, ai ≠ bi) — the arguments of the swap operation.

输出描述:

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

备注:

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).