Small Palindrome

Chef has $X$ ones ($1$s) and $Y$ twos ($2$s) in his collection. He wants to arrange all of them into the **smallest possible palindrome number$^{\dagger}$** using **all** of these ones ($1$s) and twos ($2$s). Help Chef with the answer. Note: $X$ and $Y$ are both even numbers. --- $^{\dagger}$A **palindromic number** is a number that remains the same when its digits are reversed. ### Input -