baekjoon No Duplicates Bronze 1

i wanted to solve tree problem, but i can't find solution to use tree algorism

arr =  input().split()
# print(arr)
flag = 0
for i in range(len(arr)):
    for j in range(i+1, len(arr)):
        if arr[i] == arr[j]:
            flag = 1
if flag:
    print('no')
else:
    print('yes')