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

dic = {}
for i in range(n):
    dic[a[i]] = i

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

print(ans)