Extract Numbers From Specified Place In Text String

I have got cell A1 containing this text string:

=IF(SUM('SL-001 - AT-001-001'!R[852]C:R[856]C)=0,SUMPRODUCT('SL-001 - AT-001-001'!R[826]C:R[830]C,
'SL-001 - AT-001-001'!R[840]C:R[844]C,'SL-001 - AT-001-001'!R[846]C:R[850]C),
SUMPRODUCT('SL-001 - AT-001-001'!R[826]C:R[830]C,'SL-001 - AT-001-001'!R[840]C:R[844]C,
'SL-001 - AT-001-001'!R[846]C:R[850]C,'SL-001 - AT-001-001'!R[852]C:R[856]C))
*'SL-001 - AT-001-001'!R992C*R3C9
and I would like a macro that will extract the numbers between each instance of the letters R and C , i.e. 852, 856, 826 etc etc. in cells A2, A3, A4 respectively.