Formula to return first 3 numbers in account code

I have a column with a list of codes as follows,

539-K600Z28
757-K600F87
757-K0033FZ
757-K0037F1
539-k0054s8
757-0056RP

The formula

=IF(L6="","",LEFT(L6,1) + 0)

returns only the first number. I am looking for a formula that will return the first 3 numbers, in this case.

757
539

Thank You
JImO