import math
import sys
n=int(input())
s=list(map(int,input().split()))
s=list(set(s))
s.sort()
print(len(s))
for item in s:
    print(item,end=" ")

/**************************************************************
	Problem: 1765
	User: admin
	Language: Python
	Result: Accepted
	Time:51 ms
	Memory:34480 kb
****************************************************************/