Minimum Cost of Buying Candies With Discount

class Solution:
    def minimumCost(self, cost: List[int]) -> int:
        cost.sort(reverse=True)
        n = len(cost)
        cost.append(0)
        res = 0
        i = 0
        while i < n:
            res += cost[i] + cost[i+1]
            i += 3
        return res