Arithmetic operators

[askretov]

Hello!
Can somebody help with a small question, please.
I have Discovery rule and item prototypes with SNMP type. I need to write an OID with subtraction operation (-) for macro {SNMP.INDEX} :

stat.statIfwanTable.statIfwanEntry.statIfwanOctetsTx.{#SNMPINDEX}-2

In that way I receive a resulted OID as

stat.statIfwanTable.statIfwanEntry.statIfwanOctetsTx.[B][U]3-2[/U][/B]

But I need .1 instead of that.
How can I use any arithmetic operations in item fields ???

[aib]

Create an item prototype with SNMPstat.statIfwanTable.statIfwanEntry.statIfwanOc tetsTx.{#SNMPINDEX}

Create a secont Item prototype - calculated - with formula:
last("stat.statIfwanTable.statIfwanEntry.statIfwan OctetsTx.{#SNMPINDEX}")-2