WOW Factor

Recall that string $$$a$$$ is a subsequence of a string $$$b$$$ if $$$a$$$ can be obtained from $$$b$$$ by deletion of several (possibly zero or all) characters. For example, for the string $$$a$$$="wowwo", the following strings are subsequences: "wowwo", "wowo", "oo", "wow", "", and others, but the following are not subsequences: "owoo", "owwwo", "ooo".

The wow factor of a string is the number of its subsequences equal to the word "wow". Bob wants to write a string that has a large wow factor. However, the "w" key on his keyboard is broken, so he types two "v"s instead.

Little did he realise that he may have introduced more "w"s than he thought. Consider for instance the string "ww". Bob would type it as "vvvv", but this string actually contains three occurrences of "w":

• "vvvv"
• "vvvv"
• "vvvv"

For example, the wow factor of the word "vvvovvv" equals to four because there are four wows:

• "vvvovvv"
• "vvvovvv"
• "vvvovvv"
• "vvvovvv"

Note that the subsequence "vvvovvv" does not count towards the wow factor, as the "v"s have to be consecutive.

For a given string $$$s$$$, compute and output its wow factor. Note that it is not guaranteed that it is possible to get $$$s$$$ from another string replacing "w" with "vv". For example, $$$s$$$ can be equal to "vov".