diff --git a/src/medium/pow.py b/src/medium/pow.py
index d5b959f..6810ecf 100644
--- a/src/medium/pow.py
+++ b/src/medium/pow.py
@@ -10,6 +10,22 @@
 
 class Solution:
     def myPow(self, x, n):
+        if n < 0:
+            return self.myPow(1.0 / x, -n)
+        else:
+            if n == 0:
+                return 1
+            if n % 3 == 0:
+                third = self.myPow(x, n / 3)
+                return third * third * third
+            elif n % 3 == 1:
+                third = self.myPow(x, (n - 1) / 3)
+                return x * third * third * third
+            else:
+                third = self.myPow(x, (n - 2) / 3)
+                return x * x * third * third * third
+
+    def myPow_back(self, x, n):
         if n > 0:
             if n == 1:
                 return x
@@ -22,10 +38,9 @@ def myPow(self, x, n):
                 return float(1 / x)
             else:
                 return 1 / (x * (1 / self.myPow(x, n + 1)))
-        pow(2,3)
 
 
 if __name__ == "__main__":
     ss = Solution()
-    print(ss.myPow(1.001, 998))
+    print(ss.myPow(2, -2))
     print("hello imp")
diff --git a/src/medium/restore_ip_addresses.py b/src/medium/restore_ip_addresses.py
new file mode 100644
index 0000000..f1423ee
--- /dev/null
+++ b/src/medium/restore_ip_addresses.py
@@ -0,0 +1,20 @@
+#!/usr/bin/python3
+# -*- coding: utf-8 -*-
+
+"""
+    @author: loopgan
+    @contact: ganwei4955@gmail.com
+    @time: 18-8-28 下午11:51
+"""
+
+
+class Solution:
+    def restoreIpAddresses(self, s):
+        pass
+
+
+if __name__ == "__main__":
+    s = "25525511135"
+    ss = Solution()
+    print(ss.restoreIpAddresses(s))
+    print("Hello imp")