n = int(input())
a = list(map(int,input().split()))
a.sort()

dic = {}
for i in a:
    dic[i] = 1

ans = n
for i in range(1,n):
    if a[i] == a[i-1]+1:
        count = 0
        k = a[i]
        while k+count*2 in dic:
            count += 1
        ans += count

print(ans)