#include <cstdio>

 #include <cstring>

 #include <algorithm>

 #define inc(i,j,k) for(int i=j;i<=k;i++)

 #define maxn 50010

 using namespace std;

 inline int read(){

     char ch=getchar(); int f=,x=;

     while(ch<''||ch>''){if(ch=='-')f=-; ch=getchar();}

     while(ch>=''&&ch<='')x=x*+ch-'',ch=getchar();

     return f*x;

 }

 int a[maxn],b[maxn],ans,n,tot; bool c[maxn*];

 int main(){

     n=read(); inc(i,,n)a[i]=read(),c[a[i]]=; inc(i,,*n)if(!c[i])b[++tot]=i; sort(a+,a+n+);

     int p=,q=;

     while(){

         while(p<=n&&b[p]<a[q])p++; if(p==n+)break; ans++; p++; q++;

     }

     printf("%d",ans); return ;

 }