#include<iostream>
#include<algorithm>
using namespace std;
int a[110];
bool pan[110] = {0};
int main(){
	int n;
	cin >> n;
	for(int i = 0; i < n; i++) cin >> a[i];
	int ans = 0;
	for(int i = 0; i < n; i++){
		for(int j = i+1; j < n; j++){
			if(a[i] != a[j]){
				int tmp = a[i]+a[j];
				if(pan[tmp] == 1) continue;
				else{
					int q = find(a, a+n, tmp)-a;
					if(q != n){
						cout << tmp << " ";
						pan[tmp] = 1;
						ans++;
					}
				}
			}
		}
	}
	cout << ans;
	return 0;
}

救救我！