n=int(input())
a=list(map(int,input().split()))
s=[0]*1000
for i in a:
    s[i-1]+=1
sum=0
r=[]
for i in range(len(s)):
    if s[i]!=0:
        sum+=1
        r.append(i+1)
print(sum)
for i in r:
    print(i,end=' ')