diff --git a/2021/fjp1/l001.java b/2021/fjp1/l001.java
index 106487f..b1d949e 100644
--- a/2021/fjp1/l001.java
+++ b/2021/fjp1/l001.java
@@ -124,7 +124,7 @@ public ListNode mergeKLists(ListNode[] lists, int si, int ei) {
         if (si == ei)
             return lists[si];
 
-        int mid = (si + ei) / 2;
+        int mid = si + (ei-si)/2;
         ListNode l1 = mergeKLists(lists, si, mid);
         ListNode l2 = mergeKLists(lists, mid + 1, ei);
         return mergeTwoLists(l1, l2);
@@ -141,4 +141,4 @@ public static void main(String[] args) {
 
     }
 
-}
\ No newline at end of file
+}