diff --git a/godoc/godoc.go b/godoc/godoc.go
index 8ec731c..60a6a86 100644
--- a/godoc/godoc.go
+++ b/godoc/godoc.go
@@ -98,6 +98,9 @@ func (p *Presentation) initFuncMap() {
 
 		// formatting of Notes
 		"noteTitle": noteTitle,
+
+		// Number operation
+		"multiply": multiply,
 	}
 	if p.URLForSrc != nil {
 		p.funcMap["srcLink"] = p.URLForSrc
@@ -110,6 +113,8 @@ func (p *Presentation) initFuncMap() {
 	}
 }
 
+func multiply(a, b int) int { return a * b }
+
 func filenameFunc(path string) string {
 	_, localname := pathpkg.Split(path)
 	return localname
</div><div class="naked_ctrl">
<form action="/index.cgi/larger-text" method="get" name="gate">
<p><a href="http://altstyle.alfasado.net">AltStyle</a> によって変換されたページ <a href="https://patch-diff.githubusercontent.com/raw/golang-china/golangdoc/pull/9.diff">(-&gt;オリジナル)</a>
/ <label>アドレス: <input type="text" name="naked_post_url" value="https://patch-diff.githubusercontent.com/raw/golang-china/golangdoc/pull/9.diff" size="22" /></label> <label>モード: <select name="naked_post_mode">
<option value="default">デフォルト</option>
<option value="speech">音声ブラウザ</option>
<option value="ruby">ルビ付き</option>
<option value="contrast">配色反転</option>
<option value="larger-text" selected="selected">文字拡大</option>
<option value="mobile">モバイル</option>
</select>
<input type="submit" value="表示" />
</p>
</form>
</div>