card_num = int(input())
card_list = list(map(int, input().split()))

card_set = set(card_list)

sum = 0
for loop_i in range(card_num):
    one_before_card = card_list[loop_i] - 1
    if one_before_card not in card_set: sum += card_list[loop_i]

print(sum)