Create a function in python3 called valid_check without import that will validate a math expression:

Initialize the counter to 0.

When you see a literal, increment the counter. such as (x,y,z)

When you see a binary operator, decrement the counter twice, then increment it. (+,*)

When you see a unary operator, decrement the counter, then increment it.( ~)

At the end of the string, if the counter is 1, and if it never went below 0, the string is valid.