Finding numbers left in list

Column M represent the numbers, column O is the "constant" list of numbers, and column P is the sort of numbers LEFT in the list:


M1: 79 O1: 80 P1: 81
M2: 82 O2: 81 P2: 40
M3: 34 O3: 34 P3: 45
M4: 80 O4: 35 P4:
M5: 46 O5: 40 P5:
M5: 35 O6: 45 P6:
O7: 46 P7:
O8: 79 P8:
O9: 82 P9:

In Col P I was working on this coding below, but I'm getting an "#VALUE" message. What am I missing?

=IF(FIND($M$1:$M$5,O1,1),O1="")

Try this
In a spare column (R in the attached)
In R1

=IF(ISNUMBER(MATCH(O1,$M$1:$M$9,0)),"",O1)

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In P1 this array formula

=IF(ROW()-ROW($P$1:$P$1000)+1>ROWS($R$1:$R$1000)-COUNTBLANK($R$1:$R$1000),"",INDIRECT(ADDRESS(SMALL((IF($R$1:$R$1000<>"",ROW($R$1:$R$1000),ROW()+ROWS($R$1:$R$1000))),ROW()-ROW($P$1:$P$999)+1),COLUMN($R$1:$R$1000),4)))

Confirm with Ctrl+Shift+Enter not just Enter
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This last formula removes the blanks from Column R (Helper Column can be hidden), you might not need it.

Hope this helps