Lucy has got the task to create badges for all students of the school. A badge is created by superimposing two squares. The bottom square should be of blue colour and top square should be of yellow colour. The squares must be rotated in such a way that the projection of the badge displays 8 distinguishable vertices.

Please help Lucy find out the maximum number of badges she can make with available n squares.

Input Format:
The first line of input file contains integer n. Each of the next n lines contain two space separated integers, ci and di. ci is the colour number and di is the length of side of square

Output Format:
Print the maximum number of badges that can be made.

Constraints:
1 <= n <= 100000
1 <= di <= 1000
1 <= ci <= 2

Notes:
- ci = 1 denotes blue color and vice-versa.

Problem Statement in native Language: http://hck.re/xepWPj