# https://qiita.com/fumitoh/items/3b677522e24ac0235bd0

import itertools

N = int(input())
A = sorted([int(x) for x in input().split()])
group = [list(g) for _, g in itertools.groupby(A, key=lambda n, c=itertools.count(): n - next(c))]
# print(A)
# print(group)
# result = 0
# for x in group:
#     result += x[0]

print(sum([x[0] for x in group]))