diff --git a/problem03.rb b/problem03.rb
index e69de29..601277c 100644
--- a/problem03.rb
+++ b/problem03.rb
@@ -0,0 +1,15 @@
+def smallest_prime_factor(num)
+  return 2 if num.even?
+  i = 3
+  while i <= num
+    return i if num%i==0
+    i += 2
+  end
+end
+
+def largest_prime_factor(num)
+  return num if smallest_prime_fasctor(num) == num
+  largest_prime_factor(num/smallest_prime_factor(num))
+end
+
+p largest_prime_factor(600851475143)