Interesting Product

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 $d$.

Input

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 $d$).

Output

Print the number of possible product values.

Examples