Beautiful fountains rows
题目描述
Butler Ostin wants to show Arkady that rows of odd number of fountains are beautiful, while rows of even number of fountains are not.
The butler wants to show Arkady n gardens. Each garden is a row of m cells, the i-th garden has one fountain in each of the cells between li and ri inclusive, and there are no more fountains in that garden. The issue is that some of the gardens contain even number of fountains, it is wrong to show them to Arkady.
Ostin wants to choose two integers a≤b and show only part of each of the gardens that starts at cell a and ends at cell b. Of course, only such segments suit Ostin that each garden has either zero or odd number of fountains on this segment. Also, it is necessary that at least one garden has at least one fountain on the segment from a to b.
Help Ostin to find the total length of all such segments, i.e. sum up the value (b-a+1) for each suitable pair (a,b).
The first line contains two integers n and m (1≤n,m≤2·105)− the number of gardens and the length of each garden.
n lines follow. The i-th of these lines contains two integers li and ri (1≤li≤ri≤m)− the bounds of the segment that contains fountains in the i-th garden.
Print one integer: the total length of all suitable segments.
1 5
2 4
23
3 6
2 4
3 6
4 4
19
In the first example the following pairs suit Ostin: (a,b): (1,2), (1,4), (1,5), (2,2), (2,4), (2,5), (3,3), (4,4), (4,5).
In the second example the following pairs suit Ostin: (a,b): (1,2), (1,5), (2,2), (2,5), (3,3), (4,4), (4,6), (5,5), (6,6).
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