diff --git a/day24/input b/day24/input
new file mode 100644
index 0000000..4d58b06
--- /dev/null
+++ b/day24/input
@@ -0,0 +1,300 @@
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diff --git a/day24/sample1.in b/day24/sample1.in
new file mode 100644
index 0000000..35963dc
--- /dev/null
+++ b/day24/sample1.in
@@ -0,0 +1,5 @@
+19, 13, 30 @ -2,  1, -2
+18, 19, 22 @ -1, -1, -2
+20, 25, 34 @ -2, -2, -4
+12, 31, 28 @ -1, -2, -1
+20, 19, 15 @  1, -5, -3
diff --git a/day24/sol.py b/day24/sol.py
new file mode 100644
index 0000000..13447f8
--- /dev/null
+++ b/day24/sol.py
@@ -0,0 +1,109 @@
+#!/usr/bin/env python
+def read_input(input):
+    data = []
+    for line in input:
+        x, y, z, dx, dy, dz = [int(v) for v in line.replace("@", "").replace(",", " ").split()]
+        data.append((x,y,z,dx,dy,dz))
+    return data
+
+def intersect_2d(l1, l2):
+    x0, y0, _, dx0, dy0, _ = l1
+    x1, y1, _, dx1, dy1, _ = l2
+
+    # convert to ax+by = c form
+    #(x - x0)dx0 + x0 = (y-y0)dy0 + y0
+    #x*dx0 - dx0*x0 + x0 = y*dy0 - dy0*y0 + y0
+    #x*dx0 - y*dy0 = dx0*x0 - dy0*y0 + y0 - x0
+
+    # x0 + t dx0 = x(t)
+    # y0 + t dy0 = y(t)
+    # t = (y - y0)/dy0
+    # t = (x - x0)/dx0
+    # (y-y0)/dy0 = (x-x0{
+    # x0 + (y-y0)/dy0 * dx0 = x
+    # x0 + y*dx0/dy0 - y0*dx0/dy0 = x
+    # x0 - y0*dx0/dy0 = x - y*dx0/dy0
+
+    a0 = dx0
+    b0 = -dy0
+    c0 = dx0*x0 - dy0*y0
+
+    a0 = dy0
+    b0 = -dx0
+    c0 = x0*(y0+dy0) - y0*(x0+dx0)
+
+    assert a0*x0 + b0*y0 == c0
+
+    a1 = dx1
+    b1 = -dy1
+    c1 = dx1*x1 - dy1*y1
+
+    a1 = dy1
+    b1 = -dx1
+    c1 = x1*(y1+dy1) - y1*(x1+dx1)
+    assert a1*x1 + b1*y1 == c1
+
+    # cramer's rule
+    d = a0*b1 - a1*b0
+    if d == 0 :
+        # non-intersecting
+        return None
+
+    return (c0*b1 - c1*b0)/d, (a0*c1 - a1*c0)/d
+
+def intersect_2d(l1, l2):
+    x0, y0, _, dx0, dy0, _ = l1
+    x1, y1, _, dx1, dy1, _ = l2
+
+    # convert to ax+by = c form
+    # (x-x0)/dx0 = (y-y0)/dy0
+    # dy0(x-x0) = (dx0)(y-y0)
+    # x*dy0 - dy0*x0 = y*dx0 - dx0*y0
+    # x*dy0 - y*dx0 = dy0*x0 - dx0*y0
+
+    a0 = dy0
+    b0 = -dx0
+    c0 = x0*dy0 - y0*dx0
+
+    assert a0*x0 + b0*y0 == c0
+
+    a1 = dy1
+    b1 = -dx1
+    c1 = x1*dy1 - y1*dx1
+    assert a1*x1 + b1*y1 == c1
+
+
+    # cramer's rule
+    d = a0*b1 - a1*b0
+    if d == 0 :
+        # non-intersecting
+        return None
+
+    return (c0*b1 - c1*b0)/d, (a0*c1 - a1*c0)/d
+
+def future(l1, point):
+    x,y,z, dx,dy,dz = l1
+    x0, y0 = point
+    return (dx < 0 and x0 <= x) or (dx > 0 and x0 >= x)
+
+def inbounds(point):
+    x,y = point
+    if 7 <= x <= 21 and 7 <= y <= 21: return True
+    return 200000000000000 <= x <= 400000000000000 and 200000000000000 <= y <= 400000000000000
+
+def solve(input):
+    data = read_input(input)
+    t = 0
+    for i,h1 in enumerate(data):
+        for h2 in data[i+1:]:
+            p = intersect_2d(h1, h2)
+            print(h1,h2, p)
+            if p is not None:
+                if future(h1, p) and future(h2, p):
+                    if inbounds(p):
+                        print(h1, h2, p)
+                        t += 1
+    print(t)
+
+import sys
+solve(sys.stdin)