import sys
from collections import defaultdict
def I(): return int(sys.stdin.readline().rstrip())
def LI(): return list(map(int,sys.stdin.readline().rstrip().split()))


N = I()
A = LI()
A.sort()
d = defaultdict(int)  # d[a] == 1 ⇔ a in A
for a in A:
    d[a] = 1

count = defaultdict(int)
# count[a] = A内の要素で構成された初項a、公差2の等差数列の最大の長さ
for a in A:
    count[a] = 0

for a in A:
    if count[a] == 0:
        b = a
        while d[b] == 1:
            b += 2
        r = (b-a)//2
        for i in range(a,b,2):
            count[i] = r-(i-a)//2

ans = N
for a in A:
    ans += count[a+1]

print(ans)