Note 2 - Earnings Per Share - Earnings Per Share (Details) - USD ($)	3 Months Ended
	Aug. 31, 2023	Aug. 31, 2022
Net income attributable to common stockholders	$ 1,598,020	$ 1,214,724
Weighted-average shares outstanding - basic (in shares)	28,279,701	28,279,701
Basic (in dollars per share)	$ 0.06	$ 0.04
Add: Preferred stock dividends for assumed conversion	$ 146,199	$ 109,418
Net income allocated to common stockholders	$ 1,744,219	$ 1,324,142
Incremental shares from assumed conversion of options, warrants and preferred stock, as appropriate (in shares)	3,828,053	3,826,754
Weighted average common stock outstanding - diluted (in shares)	32,107,754	32,106,455
Diluted (in dollars per share)	$ 0.05	$ 0.04