#include<bits/stdc++.h> 
using namespace std;
int main(){ 
	int n,a[52],b[30]={0},count=0;
	cin>>n;
	for(int i=0;i<n;i++){
		cin>>a[i];
	} 
	for(int i=0;i<n-1;i++){
		for(int j=i+1;j<n;j++){
			b[a[i]+a[j]]=1;
		}
	} 
	for(int i=0;i<=26;i++){
		if(0!=b[i]){
			++count;
		}
	}
	cout<<count<<endl;
	for(int i=0;i<=26;i++){
		if(0!=b[i]){
			cout<<i<<" ";
		}
	} 
	return 0;	
}
/**************************************************************
	Problem: 1334
	User: mariooo
	Language: C++
	Result: Accepted
	Time:6 ms
	Memory:2072 kb
****************************************************************/