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).




MODULE McNuggets;
FROM InOut IMPORT WriteCard, WriteString, WriteLn;
 
CONST Max = 100;
VAR a, b, c: CARDINAL;
    nugget: ARRAY [0..Max] OF BOOLEAN;
 
BEGIN
    FOR a := 0 TO Max DO
        nugget[a] := FALSE;
    END;
 
    FOR a := 0 TO Max BY 6 DO
        FOR b := a TO Max BY 9 DO
            FOR c := b TO Max BY 20 DO
                nugget[c] := TRUE;
            END;
        END;
    END;
 
    a := 100;
    REPEAT DEC(a); UNTIL NOT nugget[a];
    WriteString("Maximum non-McNuggets number: ");
    WriteCard(a, 2);
    WriteLn();
END McNuggets.