Sum only if latest value is not blank

[QooT]

Hi There,

I need help with DAX taht will show totals correctly.
In Totals I only want to have a sum of elements where last month is not blank.
Sample Table:

GROUP	ID	Month	Value
A	1	1	1
A	1	2	2
A	2	1	1
A	2	2	2
A	2	3	3
B	3	1	1
B	3	2	2
B	3	3	1
B	4	1	1
B	4	2	2

And the desired result in Matrix should be like this:

GROUP	ID	Month 1	Month 2	Month 3	Total
A TOTAL		2	4	3	6	6 Because For ID 1 lastMonth is blank so we only sum ID 2
	1	1	2		0	0 Because Last month is Blank
	2	1	2	3	6	Last Month ist not blank so we sum all months for that ID
B TOTAL		2	2	1	4	4 becasue For ID 4 last Month is blank so we only sum ID 3
	3	1	2	1	4	Last Month ist not blank so we sum all months for that ID
	4	1			0	0 Because Last month is Blank
GRAND TOTAL		4	6	4	10

[ThxAlot]

Weird Sum = 
SUMX(
    VALUES( 'Sample'[ID] ),
    CALCULATE(
        IF(
            MAX( 'Sample'[Month] )
                <> CALCULATE( MAX( 'Sample'[Month] ), REMOVEFILTERS( 'Sample'[ID] ) ),
            0,
            SUM( 'Sample'[Value] )
        )
    )
)

[sjoerdvn]

Total = IF(HASONEVALUE('Table'[Month]), SUM('Table'[Value]),
    VAR last_month=CALCULATE(MAX('Table'[Month]),ALL())
    VAR last_ids = CALCULATETABLE(VALUES('Table'[ID]), ALL(), 'Table'[Month]=last_month)
    RETURN CALCULATE(SUM('Table'[Value]), KEEPFILTERS(last_ids)) + 0
)