There are people standing in a line, numbered from to from left to right. Among these people, there are pairs of friends.

Define an interval () as friendly if and only if every pair of people within the interval are friends.

How many friendly intervals are there?

输入描述:

The first line contains two integers  and  (), representing the number of people and the number of pairs of friends, respectively.

The next  lines each contain two integers  and  (), representing a pair of friends.

It is guaranteed that there are no duplicate friend pairs in the input.

输出描述:

Output a single integer representing the number of friendly intervals.

5 9
2 3
1 3
4 5
3 5
1 2
2 4
1 5
1 4
2 5

9