diff --git a/day_3/input b/day_3/input
new file mode 100644
index 0000000..adf173d
--- /dev/null
+++ b/day_3/input
@@ -0,0 +1,300 @@
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diff --git a/day_3/main.lua b/day_3/main.lua
new file mode 100644
index 0000000..f2dd28e
--- /dev/null
+++ b/day_3/main.lua
@@ -0,0 +1,41 @@
+function find_same(first, second)
+    for c in first:gmatch('.') do
+        if string.find(second, c) ~= nil then
+            return c
+        end
+    end
+end
+
+
+function priority(char)
+    dec = string.byte(char)
+    if dec & 0x20 == 0 then
+        -- Uppercase
+        return dec - string.byte('A') + 27
+    else
+        -- Lowercase
+        return dec - string.byte('a') + 1
+    end
+end
+
+
+file = io.open('input')
+sacks = {}
+for line in file:lines() do
+    table.insert(sacks, line)
+end
+
+total = 0
+for i, sack in pairs(sacks) do
+    local mid = math.floor(string.len(sack) / 2)
+    local first = string.sub(sack, 0, mid)
+    local second = string.sub(sack, mid + 1)
+
+    local same = find_same(first, second)
+    total = total + priority(same)
+    print(same, total)
+end
+
+print(total)
+
+
diff --git a/day_3/main2.lua b/day_3/main2.lua
new file mode 100644
index 0000000..35b0d12
--- /dev/null
+++ b/day_3/main2.lua
@@ -0,0 +1,42 @@
+function find_same(first, second, third)
+    for c in first:gmatch('.') do
+        if string.find(second, c) ~= nil and string.find(third, c) ~= nil then
+            return c
+        end
+    end
+end
+
+
+function priority(char)
+    dec = string.byte(char)
+    if dec & 0x20 == 0 then
+        -- Uppercase
+        return dec - string.byte('A') + 27
+    else
+        -- Lowercase
+        return dec - string.byte('a') + 1
+    end
+end
+
+
+file = io.open('input')
+sacks = {}
+for line in file:lines() do
+    table.insert(sacks, line)
+end
+
+total = 0
+for i = 1, math.floor(#sacks / 3) do
+    local i0 = i - 1
+    local first  = sacks[i0 * 3 + 1]
+    local second = sacks[i0 * 3 + 2]
+    local third  = sacks[i0 * 3 + 3]
+
+    local same = find_same(first, second, third)
+    total = total + priority(same)
+    print(same, total)
+end
+
+print(total)
+
+