diff --git a/Problem1.java b/Problem1.java
index 8b137891..dc51aef8 100644
--- a/Problem1.java
+++ b/Problem1.java
@@ -1 +1,22 @@
+// Given a sorted array arr[] of n-1 integers,
+//  these integers are in the range of 1 to n. There are no duplicates in the array. One of the integers is missing in the array.
+//  Find the missing integer.
 
+
+class Solution {
+    int missingNumber(int[] arr, int n) {
+        int low = 0, high = n - 2; // since size = n-1
+
+        while (low <= high) {
+            int mid = low + (high - low) / 2;
+
+            // Expected value at mid index = mid + 1
+            if (arr[mid] == mid + 1)
+                low = mid + 1;
+            else
+                high = mid - 1;
+        }
+
+        return low + 1; // the missing number
+    }
+}