<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def first_currency():
 """ Returns the id for the first currency The `default` parameter of a foreign key *MUST* be a primary key (and not an instance), else migrations break. This helper method exists solely for that purpose. """

    ct = CurrencyType.objects.filter(code='PES').first()
    if ct:
        return ct.pk