#include<stdio.h>

int a[101],b[1001];
int main()
{
	int i,n,t,c=0;
	scanf("%d",&n);
	for(i=1;i<=n;i++){
		scanf("%d",&a[i]);
		t=a[i];
		if(b[t]==0){
			c++;
		}
		b[t]++;
		
	}
	printf("%d\n",c);
	for(i=0;i<=1000;i++){
		if(b[i]>0){
			printf("%d\n",i);
		}
		
	}
	return 0;
}


/**************************************************************
	Problem: 1183
	User: admin
	Language: C
	Result: Accepted
	Time:12 ms
	Memory:1148 kb
****************************************************************/