diff --git a/README.md b/README.md
index 463f521..965e5b3 100644
--- a/README.md
+++ b/README.md
@@ -24,7 +24,7 @@ chmod +x run.sh
 out/RealTek-r8169/
 ├── INDEX.md              # оглавление со ссылками на главы
 ├── chapters/             # одна глава = один файл
-│   ├── 01-features.md
+│   ├── 00001-features.md
 │   └── ...
 └── assets/               # embedded PNG + page PNG для сломанных layout-страниц
 ```
diff --git a/extract.py b/extract.py
index 14c3192..364ba75 100644
--- a/extract.py
+++ b/extract.py
@@ -24,6 +24,7 @@ MIN_CELL_LEN_FOR_DEDUP = 4
 SPACED_LETTERS = re.compile(r"^([A-Z](?: [A-Z]){1,}|[A-Z])$")
 DEFAULT_PAGE_DPI = 150
 DEFAULT_CHAPTER_LEVEL = 2
+SECTION_INDEX_WIDTH = 5
 
 
 def slugify(title: str) -> str:
@@ -320,9 +321,9 @@ def convert(
     if preamble_pages:
         sections.append(
             {
-                "num": "00",
+                "num": f"{0:0{SECTION_INDEX_WIDTH}d}",
                 "title": "front-matter",
-                "slug": "00-front-matter",
+                "slug": f"{0:0{SECTION_INDEX_WIDTH}d}-front-matter",
                 "pages": preamble_pages,
             }
         )
@@ -339,9 +340,12 @@ def convert(
             continue
         sections.append(
             {
-                "num": f"{index:02d}",
+                "num": f"{index:0{SECTION_INDEX_WIDTH}d}",
                 "title": entry["title"],
-                "slug": f"{index:02d}-{slugify(' - '.join((*entry['parents'], entry['title'])))}",
+                "slug": (
+                    f"{index:0{SECTION_INDEX_WIDTH}d}-"
+                    f"{slugify(' - '.join((*entry['parents'], entry['title'])))}"
+                ),
                 "pages": pages,
             }
         )