#include<fstream>
#include<algorithm>
//#include<cmath>
//#include<cstdio>
#define dim 50009
using namespace std;
int a[dim],uz[dim],nr,m,b[dim],n;
int main()
{
    ifstream f("economie.in");
    ofstream g("economie.out");
    f>>n;
    for(int i=1;i<=n;i++)
    f>>a[i];
    sort(a,a+n+1);
    m=a[n];
    uz[0]=1;
    for(int i=1;i<=n;i++)
    if(!uz[a[i]])
    {
        for(int j=1;j<=m;j++)
        if(a[i]<=j)
        uz[j]=1;
        nr++;
        b[nr]=a[i];
    }
    g<<nr<<"\n";
    for(int i=1;i<=nr;i++)
    g<<b[i]<<"\n";
}