diff --git a/MOD.py b/MOD.py
new file mode 100644
index 0000000..c56918d
--- /dev/null
+++ b/MOD.py
@@ -0,0 +1,9 @@
+#Calculate (x ** y) % z efficiently.
+def pow_mod(x, y, z):
+    number = 1
+    while y:
+        if y & 1:
+            number = number * x % z
+        y >>= 1
+        x = x * x % z
+    return number