Little Ruins is a studious boy, recently he learned addition operation! He was rewarded some number bricks of $1$ to $9$ and infinity bricks of addition mark '+' and equal mark '='.
Now little Ruins is puzzled by those bricks because he wants to put those bricks into as many different addition equations form $x + y = z$ as possible. Each brick can be used at most once and x, y, z are one digit integer.
As Ruins is a beginer of addition operation, $x$, $y$ and $z$ will be single digit number.
Two addition equations are different if any number of $x$, $y$ and $z$ is different.
Please help little Ruins to calculate the maximum number of different addition equations.