import sys


class Task4:
    def __init__(self):
        self.data = []
        self.pages = 0
        self.bent_pages = 0
        self.pages_sum = 0
        self.pages_temp_sum = 0

    def write_in_data(self):
        file = open('book.in')
        self.data = [i.split('\n')[0] for i in file.readlines()]
        self.pages = int(self.data[0].split()[0])
        self.bent_pages = int(self.data[0].split()[1])
        self.data.pop(0)
        self.data = [int(i) for i in self.data]
        if 1 <= self.bent_pages <= 10 ** 4:
            pass
        else:
            sys.exit(0)

    def main(self):
        self.write_in_data()
        temp_arr = []
        for i in range(self.pages, 1, -1):
            temp_arr.append(i)
        for j in range(len(temp_arr), 0, -1):
            for d in self.data:
                if j == d:
                    temp_arr.pop(j)
        for l in temp_arr:
            self.pages_sum += l
        for i in self.data:
            self.pages_temp_sum += self.bent_pages * i
        self.write_in_file()

    def write_in_file(self):
        file = open('book.out', 'w')
        file.write(str(self.pages_sum - self.pages_temp_sum))


obj = Task4()
obj.main()