I transferred stock to constitute an IRA to Roth conversion of $89K. I want to partial recharacterize $6K of that transfer. How many shares do I need to transfer back?

I transferred 538 shares of X stock, 1997 shares of Y stock and 304 shares of Z stock on 12/21/17 from my IRA to my Roth IRA to constitute a $89,127.85 IRA to Roth conversion.  The end of day value of my Roth account on 12/21/17 was $271,895.67.  I now realize I would be better off tax wise if I had only converted $83,346.85, and want to recharacterize $6,781.  The value of my Roth account today is $290,856.34.  I want to have the custodian transfer shares of Y company stock back to the IRA to accomplish the partial recharacterization.  If the price of Y shares on the day of the original transfer was $8.74/share, and the price today is $8.95/share, how many shares of Y company stock do I need to have the custodian transfer between accounts to effect a $6,781 recharacterization?