diff --git a/missing number.py b/missing number.py
new file mode 100644
index 00000000..2ce254a1
--- /dev/null
+++ b/missing number.py	
@@ -0,0 +1,20 @@
+class Solution:
+    def missingNumber(self, arr):
+        # code here
+        
+        l=0
+        h=len(arr)-1
+        if arr[0]!=1:
+            return 1
+        if arr[-1]!=n:
+            return n
+        
+        while l<h:
+            m=(l+h)//2
+            
+            if arr[m]-m==1:
+                l=m+1
+            else:
+                h=m
+        return l+1
+            
\ No newline at end of file