AtCoder Beginner Contest 082 C - Good Sequence

from collections import defaultdict

N=int(input())
a=list(map(int,input().split()))

di=defaultdict(int)

for i in a: di[i]+=1

lost=0
for key,kosu in di.items():
    #print(key,kosu)

    if kosu<key:
        lost+=kosu
    elif kosu==key:
        pass
    else:
        lost+=(kosu-key)


print(lost)