#include<stdio.h>
int v[50001];
int s[1001];
int main()
{
	freopen("economie.in","r",stdin);
	freopen("economie.out","w",stdout);
	int n,i,j,x,max=0,p=0;
	scanf("%d",&n);
	for(i=0;i<n;++i)
	{
		scanf("%d",&x);
		v[x]=-1;
		if(x>max) max=x;
	}
	for(i=1;i<max;++i)
	{
		if(v[i]==-1)
		{
			for(j=i;j<=max-i;++j)
				if(v[j]) v[j+i]=1;
			s[p++]=i;
		}
	}
	printf("%d\n",p);
	--p;
	for(;p>=0;--p) printf("%d\n",s[p]);
	return 0;
}