diff --git a/2018/day4.py b/2018/day4.py
new file mode 100644
index 0000000..7fdc3e8
--- /dev/null
+++ b/2018/day4.py
@@ -0,0 +1,58 @@
+import re
+from collections import defaultdict
+from datetime import datetime
+
+
+def main():
+    with open("day4.txt", "rt") as f:
+        lines = [line.rstrip() for line in f.readlines()]
+    entries = [parse_entry(line) for line in lines]
+    entries = sorted(entries, key=lambda e: e[0])
+
+    sleepz = defaultdict(int)
+    noight = defaultdict(lambda: [0] * 60)
+    for t, v in entries:
+        if not isinstance(v, bool):
+            guard = v
+        elif v == False:
+            sleep_t = t
+        elif v == True:
+            sleep_d = t - sleep_t
+            sleep_minutes = sleep_d.seconds // 60
+            sleepz[guard] += sleep_minutes
+            for i in range(sleep_minutes):
+                noight[guard][sleep_t.minute + i] += 1
+    lazy_g = max(sleepz, key=lambda k: sleepz[k])
+    print("Laziest guard:", lazy_g)
+    sleepiest_min = max(range(60), key=lambda m: noight[lazy_g][m])
+    print("Sleepiest minute:", sleepiest_min)
+    print("Part 1:", lazy_g * sleepiest_min)
+
+    reliable_v = -1
+    for g in noight:
+        sleepiest_min = max(range(60), key=lambda m: noight[g][m])
+        sleepiest_v = noight[g][sleepiest_min]
+        if sleepiest_v > reliable_v:
+            reliable_g = g
+            reliable_m = sleepiest_min
+            reliable_v = sleepiest_v
+    print("Part 2:", reliable_g * reliable_m)
+
+
+LINE_RE = re.compile(r"^\[([^\]]+)\] (.+)$")
+
+def parse_entry(line):
+    match = LINE_RE.match(line)
+    ts, content = match.groups()
+    dt = datetime.fromisoformat(ts)
+    if content.startswith("Guard"):
+        v = int(content.split()[1][1:])
+    elif content.startswith("w"):
+        v = True
+    elif content.startswith("f"):
+        v = False
+    return (dt, v)
+
+
+if __name__ == "__main__":
+    main()