MTG

Apologies if this is the wrong place to post this.

If I have a Hardened Scales and an Ozolith, the Shattered Spire on the battlefield and I cast a spell that causes a creature to get a +1/+1 counter, do I add a total of three +1/+1 counters to that creature or four?

In other words, do Hardened Scales and Ozolith, the Shattered Spire both see the new +1/+1 counter on the stack simultaneously and add a single additional +1/+1 counter each? Or would (for example) Hardened Scales see the original +1/+1 counter, and add another one to the stack, at which point Ozolith, the Shattered Spire sees the original +1/+1 counter and adds an additional counter to the stack, and then as a separate event sees the +1/+1 counter from Hardened Scales and adds a second additional +1/+1 counter?

If the latter is true, then adding a couple other cards (like a Pir, Imaginative Rascal and Kami of Whispered Hopes) would make this insane. Hardened scales adds 1 additional +1/+1, Ozolith, the Shattered Spire adds 2 more, then Pir adds 3, then Kami of Whispered Hopes adds 4, for a total of 11 (including the original +1/+1 counter).