#include<bits/stdc++.h>
using namespace std;
int b[1001]={0};
int main()
{
	int n,sum=0;
	cin>>n;
	int m;
	for(int i=0;i<n;i++)
	{
		cin>>m;
		b[m]++;
	}
	for(int i=0;i<1001;i++)
	{
		if(b[i]!=0)
		{
			sum+=1;
		}
	}
	cout<<sum<<endl;
	for(int i=0;i<1001;i++)
	{
		if(b[i]!=0)
		{
			cout<<i<<endl;
		}
	}

	return 0;
}


/**************************************************************
	Problem: 1183
	User: lzc
	Language: C++
	Result: Accepted
	Time:11 ms
	Memory:2076 kb
****************************************************************/