Twice

Problem Background

Special for beginners, ^_^

Problem Description

Given between $2$ and $15$ positive integers, your task is to count how many pairs of numbers satisfy: one number in the pair is twice the other.

For example, given 1 4 3 2 9 7 18 22, the answer is $3$, because $2$ is twice $1$, $4$ is twice $2$, and $18$ is twice $9$.

Input Format

One line giving between $2$ and $15$ positive integers less than $100$. The input ends with a $0$.

Output Format

One integer: the number of pairs in which one number is twice the other.

Sample Input

1 4 3 2 9 7 18 22 0

Sample Output

3

Constraints

Time limit: 1s, memory limit: 1024KiB for each test case.