Find all possible values of product $i \cdot j$, if the integer values of variables $i$ and $j$ vary for $i$ from $a$ to $b$ and $j$ from $c$ to $d$. \InputFile One line contains $4$ numbers $a, b, c$ and $d$ ($1 \le a, b, c, d \le 10$, $a$ can be greater than $b$, $c$ can be greater than $d$). \OutputFile Print the number of possible product values.