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diff --git a/year2021/day1/part2.clj b/year2021/day1/part2.clj
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+; Day 1, part 2
+; Read a list of numbers from stdin, separated by newlines.
+; Count occurances of the current sum being greater than
+; the previous, where a sum is that of the current number,
+; the previous number, and the next number.
+;
+
+(let [input (->> (slurp "./in")
+                 clojure.string/split-lines
+                 (mapv read-string))]
+  (println
+    (count
+      (filter #(< (get input %) (get input (+ % 3)))
+        (range 0 (- (count input) 3))))))
+