diff --git a/lib/num_fns.py b/lib/num_fns.py
index d7cedf3..28b60ee 100644
--- a/lib/num_fns.py
+++ b/lib/num_fns.py
@@ -1,9 +1,26 @@
+import math
+
 def isDivBy(num, denom):
     return num % denom == 0
 
 def fib(i):
-    if i == 1:
-        return 1
-    elif i == 2:
-        return 2
-    return fib(i - 1) + fib(i - 2)
\ No newline at end of file
+    if i == 1: return 1
+    elif i == 2: return 2
+    return fib(i - 1) + fib(i - 2)
+
+def sieve(num):
+    prime = [True for i in range(num + 1)]
+    p = 2
+    while p * p <= num:
+        if prime[p] == True:
+            for i in range(p * p, num + 1, p):
+                prime[i] = False
+        p += 1
+
+    primes = []
+
+    for p in range(2, num + 1):
+        if prime[p]:
+            primes.append(p)
+    
+    return primes
diff --git a/src/problem3.py b/src/problem3.py
new file mode 100644
index 0000000..6ae1de6
--- /dev/null
+++ b/src/problem3.py
@@ -0,0 +1,14 @@
+import math
+import sys
+sys.path.append("lib")
+from num_fns import sieve, isDivBy
+
+target = 600851475143
+
+primes = sieve(math.floor(math.sqrt(target)))
+primes.reverse()
+
+for i in primes:
+    if isDivBy(target, i):
+        print(i)
+        break