Database
[{total:7421356},{total:79421356},{total:105457854},{total:1054578540},{total:10545785400},]
Query
db.collection.aggregate({$addFields:{length:{$multiply:[{$add:[{$strLenCP:{$toString:{$toLong:"$total"},}},-2]},-1]},}},{$project:{value:{$toLong:{$trunc:["$total","$length"],}},_id:0,}})