A Rocket having initial mass `5xx10^(6)kg` , which include mass of fuel of mass `4xx10^(6)kg`

A Rocket having initial mass `5xx10^(6)kg` , which include mass of fuel of mass `4xx10^(6)kg` is ejecting gas with velocity `4000m//s` relative to Rocket when entire fuel finishes?

`4xx10^(6)kg`