diff --git a/2021/22.js b/2021/22.js
new file mode 100644
index 0000000..59e7e2f
--- /dev/null
+++ b/2021/22.js
@@ -0,0 +1,66 @@
+class Cuboid {
+    constructor(sgn, xs, xe, ys, ye, zs, ze) {
+        this.sgn = sgn
+        this.xs = Math.min(xs, xe)
+        this.xe = Math.max(xs, xe)
+        this.ys = Math.min(ys, ye)
+        this.ye = Math.max(ys, ye)
+        this.zs = Math.min(zs, ze)
+        this.ze = Math.max(zs, ze)
+    }
+
+    vol() { return (this.xe - this.xs + 1) * (this.ye - this.ys + 1) * (this.ze - this.zs + 1) }
+
+    int(that) {
+        if (that.xe < this.xs || this.xe < that.xs) return
+        if (that.ye < this.ys || this.ye < that.ys) return
+        if (that.ze < this.zs || this.ze < that.zs) return
+
+        let sgn = -that.sgn
+
+        let xs = Math.max(this.xs, that.xs)
+        let xe = Math.min(this.xe, that.xe)
+        let ys = Math.max(this.ys, that.ys)
+        let ye = Math.min(this.ye, that.ye)
+        let zs = Math.max(this.zs, that.zs)
+        let ze = Math.min(this.ze, that.ze)
+
+        return new Cuboid(sgn, xs, xe, ys, ye, zs, ze)
+    }
+}
+
+function day20(input, part2) {
+    let lines = input.split`\n`
+
+    let cuboids = []
+
+    for (let line of lines) {
+        let data = line.match(/^(.+) x=(.+)\.\.(.+),y=(.+)\.\.(.+),z=(.+)\.\.(.+)$/)
+        let cuboid = new Cuboid(data[1] == "on", +data[2], +data[3], +data[4], +data[5], +data[6], +data[7])
+
+        if (!part2 && (
+            cuboid.xs < -50 || cuboid.xe > 50 ||
+            cuboid.ys < -50 || cuboid.ye > 50 ||
+            cuboid.zs < -50 || cuboid.ze > 50)) {
+            continue
+        }
+
+        let toAdd = [cuboid]
+
+        for (let otherCuboid of cuboids) {
+            let intersection = cuboid.int(otherCuboid)
+
+            if (intersection) {
+                toAdd.push(intersection)
+            }
+        }
+
+        cuboids.push(...toAdd)
+    }
+
+    return cuboids.map((e) => e.vol() * e.sgn).sum()
+}
+
+if (typeof window == "undefined") {
+    module.exports = day20
+}
diff --git a/out.js b/out.js
index a4de305..0619a0a 100644
--- a/out.js
+++ b/out.js
@@ -1244,7 +1244,7 @@ if (typeof window == "undefined" && process.argv[2] == "test") {
 
 	const year = "2021"
 
-	for (let i = +process.argv[3] || 1; i <= 21; i++) {
+	for (let i = +process.argv[3] || 1; i <= 22; i++) {
 		const func = require(`./${year}/${i}.js`)
 		const input = fs.readFileSync(`./${year}/inputs/${i}`, "utf8")
 		const answers = fs.readFileSync(`./${year}/answers/${i}`, "utf8").split("\n-----\n")
diff --git a/test.js b/test.js
index 0c8effa..6575c98 100644
--- a/test.js
+++ b/test.js
@@ -3,7 +3,7 @@ if (typeof window == "undefined" && process.argv[2] == "test") {
 
 	const year = "2021"
 
-	for (let i = +process.argv[3] || 1; i <= 21; i++) {
+	for (let i = +process.argv[3] || 1; i <= 22; i++) {
 		const func = require(`./${year}/${i}.js`)
 		const input = fs.readFileSync(`./${year}/inputs/${i}`, "utf8")
 		const answers = fs.readFileSync(`./${year}/answers/${i}`, "utf8").split("\n-----\n")