Chain of expression in Velocity

Question

I have a input like abcd/1234/rftg/74574/werf , I want to convert into output abcd_rftg_werf . I want numeric part to be removed and replaced with _ .Can some one please help

I am trying to execute below code but its not working

#foreach ($element in $input.split("/"))
    #if($element.matches("-?\\d+(\\.\\d+)?"))
        $element
    #end
#end