diff --git a/Problem1.java b/Problem1.java
index 8b137891..e6c1bb6e 100644
--- a/Problem1.java
+++ b/Problem1.java
@@ -1 +1,21 @@
 
+class Solution {
+    int missingNum(int arr[]) {
+        Arrays.sort(arr);
+        int high=arr.length-1;
+        int low =0;
+        int n=high+2;
+
+        while(low<=high){
+            int mid= low+(high-low)/2;
+
+            if(arr[mid]==mid+1){
+                low=mid+1;
+            }else{
+                high=mid-1;
+            }
+        }
+        return low+1;
+
+    }
+}
\ No newline at end of file