hashd = dict()
ans=0
n = int(input())
nums = list(map(int,input().split(" ")))
for num in nums:
    if num in hashd:
        hashd[num]+=1
    elif num not in hashd:
        hashd[num] = 1
for i in hashd:
    if i == hashd[i]:
        ans+=i
print(ans)