I'm attempting to solve a problem commonly known as the Coin problem, but using McNuggets. McNuggets come in boxes containing either 6, 9, or 20 nuggets. I want to write a python script that uses Diophantine equations to determine if a given number of McNuggets n can be exactly purchased in these groupings. For example:

• 26 McNuggets -- Possible: 1 6-pack, 0 9-packs, 1 20-pack
• 27 McNuggets -- Possible: 0 6-packs, 3 9-packs, 0 20-packs
• 28 McNuggets -- Not possible

This is my current attempt at writing the solution in Python, but the output is incorrect and I'm not sure what's wrong.

n=input("Enter the no.of McNuggets:")   
a,b,c=0,0,0   
count=0   
for a in range(n):  
    if 6*a+9*b+20*c==n:     
            count=count+1
               break
    else:  
        for b in range(n):  
            if 6*a+9*b+20*c==n:  
                count=count+1  
                break  
            else:  
                for c in range(n):  
                    if 6*a+9*b+20*c==n:  
                        count=count+1  
                        break  
if count>0:  
    print "It is possible to buy exactly",n,"packs of McNuggetss",a,b,c  
else:  
    print "It is not possible to buy"