n = 0
sum = 0

DO
    INPUT "Enter integral rainfall (99999 to quit): ", i
    IF i = 99999 THEN
        EXIT DO
    ELSEIF (i < 0) OR (i <> INT(i)) THEN
        PRINT "Must be an integer no less than 0, try again."
    ELSE
        n = n + 1
        sum = sum + i
        PRINT "  The current average rainfall is"; sum / n
    END IF
LOOP