Mo. Rev. Stat. § 275.120

Such associations may also have power, and they are hereby authorized to purchase and retire shares of their own stock, whether with or without par value, at a consideration not in excess of the amount for which such share, or shares, were issued in the first instance, together with interest at the rate of six percent per annum upon such shares from date of issuance thereof, less, however, the amount of dividends, if any, paid to the holder of such shares.