from collections import Counter
input()
nums=list(map(int,input().split()))
ans=0
prev_cnt=0
prev_key=-1
cnt=Counter(nums)
for i in sorted(cnt.keys()):
    if prev_key+1!=i:
        prev_cnt=0
    ans+=max(0,cnt[i]-prev_cnt)
    prev_key=i
    prev_cnt=cnt[i]
print(ans)

1.统计每个数字出现的次数

2.按顺序遍历

3.计算代价