Use MyDocuments in PowerShell

How do I make these two lines of PowerShell into one:

$tmp=([Environment]::GetFolderPath("MyDocuments"))
mkdir $tmp\foo\bar

PowerShell seamse to treat this as two lines if i try:

mkdir ([Environment]::GetFolderPath("MyDocuments"))\foo\bar

>Solution :

Better use PowerShell cmdlets specially designed for that:

New-Item -Path (Join-Path -Path ([Environment]::GetFolderPath("MyDocuments")) -ChildPath "foo\bar") -ItemType Directory -Force