Powershell: Obtain System Uptime

$operatingSystem = Get-WmiObject Win32_OperatingSystem
$lastboottimedate = `
[Management.ManagementDateTimeConverter]::ToDateTime($operatingSystem.LastBootUpTime)
$currentdate = `
[Management.ManagementDateTimeConverter]::ToDateTime($operatingSystem.localDateTime)
$up = $currentdate-$lastboottimedate
$uptime = "System has been up for " + $up.Days + " Days " + $up.Hours + `
" Hours " + $up.Minutes + " Minutes " + $up.Milliseconds + " Milliseconds"
$uptime