Add counting in this plsql:
```plsql
SELECT
    DISTINCT papf.person_id,
    papf.employee_number,
    papf.current_employee_flag,
    papf.sex,
    papf.title,
    papf.full_name,
    papf.first_name,
    papf.email_address,
    papf.date_of_birth,
    papf.office_number,
    papf.work_telephone,
    papf.national_identifier
FROM apps.per_all_people_f papf,
        apps.per_all_assignments_f paaf,
        apps.per_grades pg
WHERE paaf.person_id = papf.person_id
    AND pg.grade_id = paaf.grade_id
    AND pg.grade_id IN (
        SELECT grade_id FROM apps.per_grades
        WHERE name LIKE 'Locum%'
    )
    AND TRUNC(sysdate) BETWEEN paaf.effective_start_date AND paaf.effective_end_date
    AND TRUNC(sysdate) BETWEEN papf.effective_start_date AND papf.effective_end_date
    AND UPPER(papf.last_name) = UPPER('CHAN')
    AND UPPER(papf.national_identifier) LIKE UPPER('E771')||'%';
        
```