189 B

#include<bits/stdc++.h>
int n,a[1000007],cnt,i;int main(){scanf("%d",&n);for(i=1;i<=n;i++)scanf("%d",&a[i]);std::sort(a+1,a+n+1);for(int i=1;i<=n;i++)if(a[i]<=i)cnt++;printf("%d",day);}