Neat String interpolation

foreach(file in files){
//Process file
Console.WriteLine($"Processed File [{file.Nr}/{files.Count}]");
}

foreach(file in files){
//Process file
Console.WriteLine($"Processed File [{file.Nr}/{files.Count}]");
}

I have this little something, and I want the counter to stay fixed width so

[ 1/50]

[ 1/50]

instead of

[1/50]

[1/50]

how can I do this ?
As simple as possible, I just want it to look neat not write a TUI framework.

I found

$"{val , fixedWidth}"

$"{val , fixedWidth}"

but that only works with constants so it can't adapt if I reach 100 files.