Previous Period MDX for universe

Hello Friends Please help me with MDX Syntax, I want to derive the previous period revenue so I want to write the MDX in where clause in universe..

My current period works fine as below syntax , please edit to make it prior period = current user prompt entered period - 1

<FILTER KEY="[ZFISCPER].[LEVEL01]">

<CONDITION OPERATORCONDITION="Equal">

<CONSTANT NAME="@Prompt('Select Fiscal Month','A','Period\Fiscal Month', mono,constrained) "/>

</CONDITION></FILTER>

If I write -1 as below it throw syntax error in webi please correct it

<FILTER KEY="[ZFISCPER].[LEVEL01]">

<CONDITION OPERATORCONDITION="Equal">

<CONSTANT NAME="@Prompt('Select Fiscal Month','A','Period\Fiscal Month', mono,constrained) - 1 "/>

</CONDITION></FILTER>

Thanks

Soniya