diff --git a/slides/count-slides.py b/slides/count-slides.py
index 3b0f5aa9..6643d3ba 100755
--- a/slides/count-slides.py
+++ b/slides/count-slides.py
@@ -1,57 +1,75 @@
 #!/usr/bin/env python
 import re
 import sys
+import yaml
+
+FIRST_SLIDE_MARKER = "name: toc-"
+PART_PREFIX = "part-"
+
+filename = sys.argv[1]
+if filename.endswith(".html"):
+    html_file = filename
+    yaml_file = filename[: -len(".html")]
+else:
+    html_file = filename + ".html"
+    yaml_file = filename
+excluded_classes = yaml.safe_load(open(yaml_file))["exclude"]
 
-PREFIX = "name: toc-"
-EXCLUDED = ["in-person"]
 
 class State(object):
     def __init__(self):
-        self.current_slide = 1
-        self.section_title = None
-        self.section_start = 0
-        self.section_slides = 0
+        self.current_slide = -1
         self.parts = {}
-        self.sections = {}
-    def show(self):
-        if self.section_title.startswith("part-"):
-            return
-        print("{0.section_title}\t{0.section_start}\t{0.section_slides}".format(self))
-        self.sections[self.section_title] = self.section_slides
+
+    def end_section(self):
+        if state.section_title:
+            print(
+                "{0.section_start}\t{0.section_slides}\t{0.section_title}".format(self)
+            )
+        if self.section_part:
+            if self.section_part not in self.parts:
+                self.parts[self.section_part] = 0
+            self.parts[self.section_part] += self.section_slides
+
+    def new_section(self, slide):
+        # Normally, the title should be prefixed by a space
+        # (because section titles are first-level titles in markdown,
+        # e.g. "# Introduction", and markmaker removes the # but leaves
+        # the leading space).
+        self.section_title = None
+        if "\n " in slide:
+            self.section_title = slide.split("\n ")[1].split("\n")[0]
+        toc_links = re.findall("\(#toc-(.*)\)", slide)
+        self.section_part = None
+        for toc_link in toc_links:
+            if toc_link.startswith(PART_PREFIX):
+                self.section_part = toc_link
+        self.section_start = self.current_slide
+        self.section_slides = 0
+
 
 state = State()
+state.new_section("")
+print("{}\t{}\t{}".format("index", "size", "title"))
 
-title = None
-for line in open(sys.argv[1]):
-    line = line.rstrip()
-    if line.startswith(PREFIX):
-        if state.section_title is None:
-            print("{}\t{}\t{}".format("title", "index", "size"))
-        else:
-            state.show()
-        state.section_title = line[len(PREFIX):].strip()
-        state.section_start = state.current_slide
-        state.section_slides = 0
-    if line == "---":
+for slide in open(html_file).read().split("\n---\n"):
+    excluded = False
+    for line in slide.split("\n"):
+        if line.startswith("class:"):
+            for klass in excluded_classes:
+                if klass in line.split():
+                    excluded = True
+    if excluded:
+        continue
+    if FIRST_SLIDE_MARKER in slide:
+        # A new section starts. Show info about the part that just ended.
+        state.end_section()
+        state.new_section(slide)
+    state.section_slides += 1
+    for sub_slide in slide.split("\n--\n"):
         state.current_slide += 1
-        state.section_slides += 1
-    if line == "--":
-        state.current_slide += 1
-    toc_links = re.findall("\(#toc-(.*)\)", line)
-    if toc_links and state.section_title.startswith("part-"):
-        if state.section_title not in state.parts:
-            state.parts[state.section_title] = []
-        state.parts[state.section_title].append(toc_links[0])
-    # This is really hackish
-    if line.startswith("class:"):
-        for klass in EXCLUDED:
-            if klass in line:
-                state.section_slides -= 1
-                state.current_slide -= 1
-
-state.show()
+else:
+    state.end_section()
 
 for part in sorted(state.parts, key=lambda f: int(f.split("-")[1])):
-    part_size = sum(state.sections[s] for s in state.parts[part])
-    print("{}\t{}\t{}".format("total size for", part, part_size))
-
+    print("{}\t{}\t{}".format(0, state.parts[part], "total size for " + part))