def address1(nom, cognom):
    return nom+'.'+cognom + '@student.upc.edu'

def address2(nom, cognom):
    return nom[:10]+'.'+cognom[:15] + '@student.upc.edu'

def valid_address(s):
    if s.count('@') != 1:
        return False
    else:
        return s.index('@') > 1

def generate_password(nom, cognom, dni):
    return nom[:3] + cognom[:3]+ dni[-3:-1]