convert date dd/mm/yyyy format from a form to timestamp?

convert date dd/mm/yyyy format from a form to timestamp?

I have a form requiring date in dd/mm/yyyy format and I've tried to
convert it to a timestamp with strtotime() function
but I've seen it works only if you fill the form with date written like
dd-mm-yyyy
how could i solve? I don't know abroad but here in Italy nobody writes
dates like that dd-mm-yyyy