N = int(input())
A = list(map(int, input().split()))
lst = [True] * 100
for a in A:
    lst[a] = False
ans = 0
for i in range(max(A) - 1, min(A) - 2, -1):
    # print(f"idx = {i}")
    if lst[i] and not lst[i + 1]:
        # print(i)
        ans += i + 1
print(ans)