Little Chris is having a nightmare. Even in dreams all he thinks about is math. Chris dreams about m binary strings of length n , indexed with numbers from 1 to m . The most horrifying part is that the bits of each string are ordered in either ascending or descending order. For example, Chris could be dreaming about the following 4 strings of length 5: The Hamming distance H(a, b) between two strings a and b of length n is the number of positions at which the corresponding symbols are different. Сhris thinks that each three strings with different indices constitute a single triple. Chris's delusion is that he will wake up only if he counts the number of such string triples a , b , c that the sum H(a, b) + H(b, c) + H(c, a) is maximal among all the string triples constructed from the dreamed strings. Help Chris wake up from this nightmare!

输入描述:

The first line of input contains two space-separated integers n and m (1 ≤ n ≤ 109; 3 ≤ m ≤ 105), the length and the number of strings. The next m lines contain the description of the strings. The i-th line contains two space-separated integers si and fi (0 ≤ si ≤ 1; 1 ≤ fi ≤ n), the description of the string with index i; that means that the first fi bits of the i-th string are equal to si, and the remaining n - fi bits are equal to 1 - si. There can be multiple equal strings in Chris's dream.

输出描述:

Output a single integer, the number of such string triples among the given that the sum of the Hamming distances between the strings of the triple is maximal.