Room Assignment

An elementary school is going on a three day field trip. Every student from grade 1 to grade 6 needs a room, and the rules are these.

• Grades 1 and 2 share a room with no separation by gender and no separation by grade.
• Grades 3 and 4 share a room with no separation by grade, but boys stay with boys and girls stay with girls.
• Grades 5 and 6 follow the same rule as grades 3 and 4.
• A room may hold a single student.

Given the largest number of students $K$ that one room holds, write a program that finds the minimum number of rooms needed to place every student under these rules.

For example, if the students on the trip are counted as below and $K = 2$, then 9 rooms are needed.

The first line has the number of students on the trip $N$ ($1 \le N \le 1{,}000$) and the largest number of students one room holds $K$ ($1 \le K \le 1{,}000$), separated by a space.

Each of the next $N$ lines has the gender $S$ and the grade $Y$ ($1 \le Y \le 6$) of one student, separated by a space. $S$ is 0 for a girl and 1 for a boy.

Print the minimum number of rooms needed to place every student, on one line.