#include <stdio.h>
#include <algorithm>

using namespace std;

int n,m,i,j,a[1010],b[1010],c[50010],d[50010],q;

int main()
{
	freopen("economie.in","r",stdin);
	freopen("economie.out","w",stdout);
	scanf("%d",&n);
	for (i=1; i<=n; ++i) { scanf("%d",&a[i]);d[a[i]]=1; }
	sort(a+1,a+n+1);
	for (i=a[1]; i<=a[n]; ++i)
	{
		q=1;
		for (j=1; j<=m; ++j)
			if (c[i-b[j]]==1)
			{
				q=0;
				break;
			}
		if (q==1 && d[i]==1)
		{
			++m;
			b[m]=i;
		}
		c[i]=1;
	}
	printf("%d\n",m);
	for (i=1; i<=m; ++i) printf("%d ",b[i]);
	return 0;
}