In the US, standard option contracts are for 100 shares. You cannot buy a fraction of a contract.
Long stock has a positive delta (+100 per 100 shares) and a long put has a negative delta. The size of the put's delta depends primarily on its relationship to the price of the underlying (the more in-the-money it is, the higher the delta). Secondary effects would be from implied volatility and proximity to expiration.
In order to meet the requirements of this question, you need a put strategy that maintains a net -50 delta from the underlying's current price down to a price of zero. I know of no such strategy.
The only possibility that I can think of is to buy 200 shares (+200 delta) and buy one at-the-money put (-100 delta) for a net delta of +100 or a delta of +50 per 100 shares (below the strike price). That means that for every point of drop below the strike, the total position will lose 100 delta or $100 which is a 50% hedge. Note that this ignores the cost of the put in the hedge ratio calculation. If an out-of-the-money put was used, for an accurate hedge ratio, you'd also have to include the 'deductible' loss (distance from the underlying's price down to the strike price of the put).
Also note that this is an expiration calculation. Prior to expiration, the net loss will be somewhat greater than 50% until the underlying collapses enough to drive the put's premium to parity (intrinsic value) and its delta to -100.