#获取输入
container = []
number = int(raw_input())
str = raw_input()
container = str.split(" ")
for i in range(len(container)):
container[i] = int(container[i])
#排序
for j in range(number-1,0,-1):
for i in range(j):
if container[i] >= container[i+1]:
max = container[i]
container[i] = container[i+1]
container[i+1] = max
#去重
new_container = []
for i in range(number-1):
if i < number-2:
if container[i] not in container[i+1:]:
new_container.append(container[i])
else:
if container[i] == container[i+1]:
new_container.append(container[i])
else:
new_container.append(container[i])
new_container.append(container[i+1])
#输出
print(len(new_container))
for i in range(len(new_container)):
if i != len(new_container)-1:
print(new_container[i],end = ' ')
else:
print(new_container[i],end = "")