diff --git a/day3/README.md b/day3/README.md
new file mode 100644
index 0000000..ff308a2
--- /dev/null
+++ b/day3/README.md
@@ -0,0 +1,48 @@
+# Day 3: Rucksack Reorganization
+
+One Elf has the important job of loading all the rucksacks with supplies for the jungle journey. Unfortunately, that
+Elf didn't quite follow the packing instructions, and so a few items now need to be rearranged.
+
+Each rucksack has two large **compartments**. All items of a given type are meant to go into exactly one of the two
+compartments. The Elf that did the packing failed to follow this rule for exactly one item type per rucksack.
+
+The Elves have made a list of all the items currently in each rucksack (your puzzle input), but they need your help
+finding the errors. Every item type is identified by a single lowercase or uppercase letter (that is, `a` and `A` refer to
+different types of items).
+
+The list of items for each rucksack is given as characters all on a single line. A given rucksack always has the same
+number of items in each of its two compartments, so the first half of the characters represent items in the first
+compartment, while the second half of the characters represent items in the second compartment.
+
+For example, suppose you have the following list of contents from six rucksacks:
+
+```
+vJrwpWtwJgWrhcsFMMfFFhFp
+jqHRNqRjqzjGDLGLrsFMfFZSrLrFZsSL
+PmmdzqPrVvPwwTWBwg
+wMqvLMZHhHMvwLHjbvcjnnSBnvTQFn
+ttgJtRGJQctTZtZT
+CrZsJsPPZsGzwwsLwLmpwMDw
+```
+
+- The first rucksack contains the items `vJrwpWtwJgWrhcsFMMfFFhFp`, which means its first compartment contains the items
+  `vJrwpWtwJgWr`, while the second compartment contains the items `hcsFMMfFFhFp`. The only item type that appears in
+  both
+  compartments is lowercase **p**.
+- The second rucksack's compartments contain `jqHRNqRjqzjGDLGL` and `rsFMfFZSrLrFZsSL`. The only item type that appears
+  in
+  both compartments is uppercase **L**.
+- The third rucksack's compartments contain `PmmdzqPrV` and `vPwwTWBwg`; the only common item type is uppercase **P**.
+- The fourth rucksack's compartments only share item type **v**.
+- The fifth rucksack's compartments only share item type **t**.
+- The sixth rucksack's compartments only share item type **s**.
+
+To help prioritize item rearrangement, every item type can be converted to a **priority**:
+
+- Lowercase item types a through z have priorities 1 through 26.
+- Uppercase item types A through Z have priorities 27 through 52.
+In the above example, the priority of the item type that appears in both compartments of each rucksack is 16 (p), 38 (
+L), 42 (P), 22 (v), 20 (t), and 19 (s); the sum of these is `157`.
+
+Find the item type that appears in both compartments of each rucksack. **What is the sum of the priorities of those item
+types?**
\ No newline at end of file
diff --git a/day3/__init__.py b/day3/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/day3/input.txt b/day3/input.txt
new file mode 100644
index 0000000..8b1be7f
--- /dev/null
+++ b/day3/input.txt
@@ -0,0 +1,300 @@
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\ No newline at end of file
diff --git a/day3/main.py b/day3/main.py
new file mode 100644
index 0000000..106164c
--- /dev/null
+++ b/day3/main.py
@@ -0,0 +1,35 @@
+from string import ascii_letters
+
+test_dataset = [
+    "vJrwpWtwJgWrhcsFMMfFFhFp",
+    "jqHRNqRjqzjGDLGLrsFMfFZSrLrFZsSL",
+    "PmmdzqPrVvPwwTWBwg",
+    "wMqvLMZHhHMvwLHjbvcjnnSBnvTQFn",
+    "ttgJtRGJQctTZtZT",
+    "CrZsJsPPZsGzwwsLwLmpwMDw",
+]
+
+
+def priority_shared_items_sum_1(data: list[str]) -> int:
+    return sum(process(line) for line in data)
+
+
+def process(rucksack: str) -> int:
+    size = len(rucksack)
+    a = rucksack[: size // 2]
+    b = rucksack[size // 2 :]
+    a = set(a)
+    b = set(b)
+    item = a.intersection(b)
+    return ascii_letters.index(item.pop()) + 1
+
+
+def read_data() -> list[str]:
+    with open("./input.txt", "r") as f:
+        return [line.strip() for line in f.readlines()]
+
+
+if __name__ == "__main__":
+    dataset = read_data()
+    res = priority_shared_items_sum_1(dataset)
+    assert res == 157, f"{res} is not the right value"