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).




#include <stdio.h>
 
int
main() {
    int max = 0, i = 0, sixes, nines, twenties;
 
loopstart: while (i < 100) {
        for (sixes = 0; sixes*6 < i; sixes++) {
            if (sixes*6 == i) {
                i++;
                goto loopstart;
            }
 
            for (nines = 0; nines*9 < i; nines++) {
                if (sixes*6 + nines*9 == i) {
                    i++;
                    goto loopstart;
                }
 
                for (twenties = 0; twenties*20 < i; twenties++) {
                    if (sixes*6 + nines*9 + twenties*20 == i) {
                        i++;
                        goto loopstart;
                    }
                }
            }
        }
        max = i;
        i++;
    }
 
    printf("Maximum non-McNuggets number is %d\n", max);
 
    return 0;
}