C# Formatting a string with string.Format("00-00-00")

I am attempting convert this string "123456" to "12-34-56".
I try to use this code but it doesn’t seem to work correctly

string.Format("123456", "00-00-00");

Can anyone help me find a suitable pattern? Thanks for any help

>Solution :

Use below

string.Format("{0:##-##-##}", 123456);

If number is represented as string the convert to int

string.Format("{0:##-##-##}", Convert.ToInt32("123456"));

The above will print the output as

12-34-56