n=int(input())
a=list(map(int,input().split()))
a.sort()
d={x:1 for x in a}
from heapq import heappush,heappop,heapify
ary={x:0 for x in a}
heapify(a)
while a:
  v=heappop(a)
  if v in ary:
    if v in d:
      d[v]+=ary[v]
    else:
      d[v]=ary[v]
  if v+1 in d:
    if v+2 in ary:
      ary[v+2]+=d[v]*d[v+1]
    else:
      ary[v+2]=d[v]*d[v+1]
      heappush(a,v+2)
#print(d)
#print(ary)
ans=sum(ary.values())+n
print(ans)