Get sum of column record that is recently added within a Stored Procedure in SQL Server

INSERT INTO studentchargeshistory (studentid,
chargesid,
chargemonth,
chargeyear,
generatedate,
chargesamount,
sessionid)
  SELECT
    StudentRoll# AS StudentID,
    extracharges.chargesid AS ChargesID,
    'August' AS ChargeMonth,
    '2014' AS ChargeYear,
    GETDATE() AS GenerateDate,
    CASE
      WHEN apply >= 1 THEN Amount
      ELSE 0
    END AS ChargeAmount,
    6 AS SessionID
  FROM ClassCharges
  INNER JOIN extracharges
    ON extracharges.chargesid = ClassCharges.ChargesID
  INNER JOIN ClassInfo
	ON ClassInfo.ClassID = ClassCharges.ClassID
  INNER JOIN ClassSection
	ON ClassSection.ClassID = ClassInfo.ClassID
  INNER JOIN studentinfo
    ON StudentInfo.ClassSectionID = ClassSection.ClassSectionID
  
  WHERE campusid = 1
  AND StudentInfo.ClassSectionID = 1
  AND extracharges.type = 'Monthly'

  AND NOT EXISTS (SELECT
    ExtraCharges.ChargesID
  FROM studentchargeshistory
  INNER JOIN extracharges
    ON extracharges.chargesid =
    studentchargeshistory.chargesid
  INNER JOIN studentinfo
    ON studentinfo.studentroll# =
    studentchargeshistory.studentid
  WHERE chargemonth = 'August'
  AND chargeyear = '2014'
  AND sessionid = 6
  AND type = 'Monthly'
  AND studentinfo.campusid = 1
  AND studentinfo.classsectionid = 1)

Now I want get sum of (if any rows affected) Charge Amount Column so that I can insert into my ledger table