Ask HN: What is the actual formula for calcuating the current price of a stock?

I have searched high and low on Google and can't find anything other than a vague explanation of how stock prices are an equilibrium where the price of stock attempts to adjust so that the number of sellers matches the number of buyers.

But what is the exact formula? If the total amount of common stock for company ABC is X and I sell 100 shares of the stock or buy a put option, what is the exact effect on the stock price (Stock goes down by $0.0000000000000000153 for example)?

Surely someone had to program this.