String Pairs with Exact Differences

You are given n strings, each of length 4, and an integer D. Your task is to count the number of pairs of strings that differ in exactly D positions.

For example, if two strings are "abcd" and "abcf", they differ in only the 4th character. If D was 1, this pair would be counted; otherwise, it would not. Note that the positions are compared one-by-one.

Input Format: The first line contains two integers n and D. The next n lines each contain a string of exactly 4 characters.

Output Format: Output a single integer, the number of valid pairs.

inputFormat

The first line contains two integers n and D separated by space.

Then follow n lines, each containing a 4-character string.

outputFormat

Output a single integer which is the number of pairs with exactly D differing positions.

sample

3 2
abcd
abcf
abdf

1