Take the minimum of all existing tags

Hi All,

I have a conversion rule in the mapping which is as mentioned below

The source sield should be mapped to the target field,but should take the minimum of the existing tag of the source,that is,

Source->Target

Take the minimum of the existing tags of the Source.

The Source may be occurring for n number of times ,I need to take the minimum of all the existing tags.

Can you please help me on this?

Thanks in advance.