#include<bits/stdc++.h>
using namespace std;
int main(){
	int i,n,a[52],s[555],k=0,j=0;
	cin>>n;
	for(i=0;i<n;i++){
		cin>>a[i];
	}
	for(i=0;i<n;i++){
		for(j=i+1;j<n;j++){
			s[k]=a[i]+a[j];
			k++;
		}
	}
	sort(s,s+k);
	cout<<k-1<<endl; 
	for(i=0;i<k;i++){
		if(s[i]!=s[i+1])
		cout<<s[i]<<" ";
		else{
			cout<<s[i+1]<<" ";
			i++;
		}
	}
	return 0; 
}
/**************************************************************
	Problem: 1334
	User: houshanglin
	Language: C++
	Result: Wrong Answer
****************************************************************/