Greedy algorithm in Python

I want c in plunder(aList, c) to equal 0.

List = [('Gold', 10, 500), ('Silver', 5, 200), ('Diamond', 2, 2000), ('Platinum', 20, 1000)]
aList = sorted(List, key =  lambda x : x[2]) # sort the list above

Gives me the sorted list based on the 3rd value of each tuple. So I get:

[('Silver', 5, 200), ('Gold', 10, 500), ('Platinum', 20, 1000), ('Diamond', 2, 2000)]

I am trying to get the plunder(aList, c) to keep subtracting the middle values of each tuple (2, 20, 10, 5) from c until c = 0.

Here is my code:

List = [('Gold', 10, 500), ('Silver', 5, 200), ('Diamond', 2, 2000), ('Platinum', 20, 1000)]
aList = sorted(List, key =  lambda x : x[2]) # sort the list above

def plunder(aList, c):
    aList[-1] = list(aList[-1])
    i = aList[-1]
    r = 0
    if c > 0 and i[1] != 0:
        c -= 1
        i[1] -=1
        r += 1
        return plunder(aList, c-r)
    elif c == 0:
        pass
        print('Done')
    else:
        return plunder(aList[:-1], c-r)

plunder(aList, 10)

But when I run it, it prints done and the new list is:

[('Silver', 5, 200), ('Gold', 10, 500), ('Platinum', 20, 1000), ['Diamond', 0, 2000]]

and also when I type c in the python shell, it tells me that c is not defined. How could I fix these issues?

Thank you