CF960A.Check the string

A has a string consisting of some number of lowercase English letters 'a'. He gives it to his friend B who appends some number of letters 'b' to the end of this string. Since both A and B like the characters 'a' and 'b', they have made sure that at this point, at least one 'a' and one 'b' exist in the string.

B now gives this string to C and he appends some number of letters 'c' to the end of the string. However, since C is a good friend of A and B, the number of letters 'c' he appends is equal to the number of 'a' or to the number of 'b' in the string. It is also possible that the number of letters 'c' equals both to the number of letters 'a' and to the number of letters 'b' at the same time.

You have a string in your hands, and you want to check if it is possible to obtain the string in this way or not. If it is possible to obtain the string, print "YES", otherwise print "NO" (without the quotes).

A 有一个由若干个小写英文字母 'a' 组成的字符串。他将该字符串交给他的朋友 B，B 在该字符串末尾添加若干个字母 'b'。由于 A 和 B 都喜欢字符 'a' 和 'b'，因此此时字符串中至少包含一个 'a' 和一个 'b'。

接着，B 将该字符串交给 C，C 在字符串末尾添加若干个字母 'c'。然而，由于 C 是 A 和 B 的好朋友，他所添加的字母 'c' 的数量等于字符串中 'a' 的数量，或者等于 'b' 的数量（或者同时等于两者）。

你手中有一个字符串，需要判断它是否可能通过上述方式得到。如果可能，输出 "YES"；否则，输出 "NO"（不带引号）。

The first and only line consists of a string $S$ ($ 1 \le |S| \le 5,000 $). It is guaranteed that the string will only consist of the lowercase English letters 'a', 'b', 'c'.

第一行且唯一一行包含一个字符串 $S$（$ 1 \le |S| \le 5,000 $）。保证该字符串仅由小写英文字母 'a'、'b'、'c' 组成。

Print "YES" or "NO", according to the condition.

根据条件输出 “YES” 或 “NO”。

Consider first example: the number of 'c' is equal to the number of 'a'.

Consider second example: although the number of 'c' is equal to the number of the 'b', the order is not correct.

Consider third example: the number of 'c' is equal to the number of 'b'.

先考虑第一个例子：“c”的数量等于“a”的数量。

再考虑第二个例子：尽管“c”的数量等于“b”的数量，但顺序不正确。

最后考虑第三个例子：“c”的数量等于“b”的数量。