407209: GYM102697 180 Boring Strings

Memory Limit：256 MB Time Limit：1 S
Judge Style：Text Compare Creator：
Submit：0 Solved：0

Description

180. Boring Stringstime limit per test1 secondmemory limit per test256 megabytesinputstandard inputoutputstandard output
This problem is worth 5 points.

You consider a string of text to be boring if it contains only "a" characters and "b" characters. For example, "abbaba" is boring, while "abcccbabc" is not boring.

Given a string, figure out whether or not it is a boring string.

Input

The only line of input contains a single string $$$s$$$, not containing spaces.

Output

If $$$s$$$ is boring, as described above, output "YES" (no quotes). Otherwise, output "NO".

ExamplesInput
aaaaaa
Output
YES
Input
ccabbabbdd
Output
NO
Input
baaaaabad
Output
NO
Input
baaaaabba
Output
YES

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