Auto sum 2 adjacent row data into 3rd row?

[Tacrier]

I have a list of people's names in column C and cost data for each person in
column M and N.

Is there was to provide a subtotal of all cost data for each person in
Column O?

i.e.:

row 1 Smith, John 100.00 440.00
row 2 Smith, John 300.00
row 3 Smith, John 40.00
row 4 Bird, Joe 50.00 500.00
row 5 Bird, Joe 450.00


Thank you in advance!

 

[Sean Timmons]

in C2, =IF(C1=C2,"",sumif(C:C,C2,M:M)+sumif(C:C,C2,N:N))