diff --git a/input/3.txt b/input/3.txt
new file mode 100644
index 0000000..253c811
--- /dev/null
+++ b/input/3.txt
@@ -0,0 +1,300 @@
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diff --git a/src/s3a.d b/src/s3a.d
new file mode 100644
index 0000000..3739203
--- /dev/null
+++ b/src/s3a.d
@@ -0,0 +1,13 @@
+module s3a;
+import util;
+
+void main() {
+    readText("input/3.txt").strip.splitter("\n")
+        .map!(line => [
+            Set!char(line[0 .. $ / 2].to!(char[])),
+            Set!char(line[$ / 2 .. $].to!(char[]))
+        ])
+        .map!(sets => sets[0].intersectWith(sets[1]).items[0])
+        .map!(c => c.isUpper ? c - 'A' + 27 : c - 'a' + 1)
+        .sum.writeln;
+}
diff --git a/src/s3b.d b/src/s3b.d
new file mode 100644
index 0000000..1e03ed6
--- /dev/null
+++ b/src/s3b.d
@@ -0,0 +1,16 @@
+module s3b;
+import util;
+
+void main() {
+    auto sets = readText("input/3.txt").strip.splitter("\n")
+        .map!(line => Set!char(line.to!(char[]))).array;
+    ulong sum = 0;
+    for (int i = 0; i < sets.length / 3; i++) {
+        char c = sets[i * 3]
+            .intersectWith(sets[i * 3 + 1])
+            .intersectWith(sets[i * 3 + 2])
+            .items[0];
+        sum += c.isUpper ? c - 'A' + 27 : c - 'a' + 1;
+    }
+    sum.writeln;
+}
\ No newline at end of file
diff --git a/src/util.d b/src/util.d
index c9d658e..83d5084 100644
--- a/src/util.d
+++ b/src/util.d
@@ -12,3 +12,52 @@ public import std.path;
 public import std.uni;
 public import std.array;
 public import std.format;
+
+/** 
+ * Simple set implementation since the stdlib doesn't really have a good one.
+ */
+struct Set(T) {
+    T[] items;
+    this(T[] items) {
+        foreach (i; items) {
+            if (!this.contains(i)) this.add(i);
+        }
+    }
+
+    bool contains(T element) {
+        return this.items.canFind(element);
+    }
+
+    bool add(T element) {
+        if (!this.items.canFind(element)) {
+            this.items ~= element;
+            return true;
+        }
+        return false;
+    }
+
+    bool remove(T element) {
+        size_t[] indexes;
+        foreach (e, i; this.items) {
+            if (e == element) indexes ~= i;
+        }
+        this.items = this.items.remove(indexes);
+        return indexes.length > 0;
+    }
+
+    Set!T intersectWith(Set!T other) {
+        T[] intersectingItems;
+        foreach (e; this.items) {
+            if (other.contains(e)) intersectingItems ~= e;
+        }
+        return Set(intersectingItems);
+    }
+
+    Set!T unionWith(Set!T other) {
+        Set!T u = Set(this.items);
+        foreach (e; other.items) {
+            u.add(e);
+        }
+        return u;
+    }
+}