Finding Distinct in Report using Formula

I never thought this can be done using formula, but yes.Please refer to here.

Scenario : We want to see total how many Account that has Opportunities.

Create one formula field in Account object with return type Number and 0 Decimal place.Place 1 at Formula field.

Example of the report below, we want to know how many Account that has Opportunity.

So we click Customize Report, Click on Unique Account -> Choose Summarize this Report ,select Sum and Apply.

Total of Account is 8.