How get first x chars from post?

[maki_69]

Hello,
I need help with my problem.
I don't know how I can get x chars from post content and display it in title on showpost page. I already edit "SHOWTHREAD_SHOWPOST" and now my title looks like this: <title>$threadinfo[prefix_plain_html] $threadinfo[title]</title>

but i want to display:
<title>$x_chars_from_post_content $threadinfo[prefix_plain_html] $threadinfo[title]</title>

Anybody can help me?