Wikipedia
The McNuggets version of the coin problem was introduced by Henri Picciotto,
who included it in his algebra textbook co-authored with Anita Wah. Picciotto
thought of the application in the 1980s while dining with his son at
McDonald's, working the problem out on a napkin. A McNugget number is
the total number of McDonald's Chicken McNuggets in any number of boxes.
In the United Kingdom, the original boxes (prior to the introduction of
the Happy Meal-sized nugget boxes) were of 6, 9, and 20 nuggets.

Task

Calculate (from 0 up to a limit of 100) the largest non-McNuggets
number (a number n which cannot be expressed with 6x + 9y + 20z = n
where x, y and z are natural numbers).




       IDENTIFICATION DIVISION.
       PROGRAM-ID.  MCNUGGETS.
 
       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01 NUGGETS.
          03 NUGGET-FLAGS     PIC X OCCURS 100 TIMES.
             88 IS-NUGGET     VALUE 'X'.
 
       01 A                   PIC 999.
       01 B                   PIC 999.
       01 C                   PIC 999.
 
       PROCEDURE DIVISION.
       BEGIN.
           MOVE SPACES TO NUGGETS.
           PERFORM A-LOOP VARYING A FROM 0 BY 6
               UNTIL A IS GREATER THAN 100.
           MOVE 100 TO A.
 
       FIND-LARGEST.
           IF IS-NUGGET(A), SUBTRACT 1 FROM A, GO TO FIND-LARGEST.
           DISPLAY 'Largest non-McNugget number: ', A.
           STOP RUN.
 
       A-LOOP.
           PERFORM B-LOOP VARYING B FROM A BY 9
               UNTIL B IS GREATER THAN 100.
 
       B-LOOP.
           PERFORM C-LOOP VARYING C FROM B BY 20
               UNTIL C IS GREATER THAN 100.
 
       C-LOOP.
           IF C IS NOT EQUAL TO ZERO, MOVE 'X' TO NUGGET-FLAGS(C).