import sys
from operator import itemgetter
from collections import defaultdict, deque
import heapq
import bisect

stdin=sys.stdin
sys.setrecursionlimit(10 ** 8)

ip=lambda: int(sp())
fp=lambda: float(sp())
lp=lambda:list(map(int,stdin.readline().split()))
sp=lambda:stdin.readline().rstrip()
Yp=lambda:print('Yes')
Np=lambda:print('No')
inf = 1 << 60
eps = 1e-9
sortkey = itemgetter(0)

###############################################################
N = ip()
A = lp()
score = [0 for _ in range(50)]
ans = 0
for get in A:
    score[get] += 1

for i in range(1,50):
    if score[i] == 1:
        if score[i - 1] == 0:
            ans += i
print(ans)