Infinite Inversions
Description
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 pi > pj.
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.
Print a single integer — the number of inversions in the resulting sequence.
Input
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.
Output
Print a single integer — the number of inversions in the resulting sequence.
Samples
2
4 2
1 4
4
3
1 6
3 4
2 5
15
Note
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).