import math
import sys
n=int(input())
m=list(map(int,input().split()))
s=set()
for i,a in enumerate(m):
    for j,b in enumerate(m):
        if i!=j:
            s.add(a+b)
print(len(s))
s=list(s)
s.sort()
for item in s:
    print(item,end=" ")
        

/**************************************************************
	Problem: 1334
	User: admin
	Language: Python
	Result: Accepted
	Time:94 ms
	Memory:34480 kb
****************************************************************/