amount of sales at the end of the month in expressions

[#1]

Good day

Following problem, I can not count the amount of sales at the end of the month in expressions in pivot table

Sum(if(Date=Aggr(Max(Date),Month),Amount,0))

or

Sum(Aggr(FirstSortedValue(Amount,-Date),Month))

it does not work

FirmID	GoodsID	Date	Amount	Month
1	1	01.01.2013	5	Jan
1	2	31.01.2013	2	Jan
1	4	28.02.2013	3	Feb
1	2	28.02.2013	1	Feb
1	1	05.03.2013	4	March