diff --git a/54d3bb4dfc75996c1c000c6d/index.js b/54d3bb4dfc75996c1c000c6d/index.js
new file mode 100644
index 0000000..f354102
--- /dev/null
+++ b/54d3bb4dfc75996c1c000c6d/index.js
@@ -0,0 +1,21 @@
+
+const midpointSum = arr => {
+  const sums = [];
+  let sum = 0;
+  sums[-1] = 0;
+  for (let i = 0; i < arr.length; ++i) {
+    sums[i] = arr[i] + sums[i-1];
+    sum += arr[i];
+  }
+  for (let i = 1; i < arr.length - 1; ++i) {
+    if (sums[i-1] === sum - sums[i]) {
+      return i;
+    }
+  }
+  return null;
+};
+
+midpointSum([-10,3,7,8,-6,-13,21]);
+midpointSum([0,0,4,0]);
+midpointSum([9,0,1,2,3,4]);
+midpointSum([4, 1, 7, 9, 3, 9]);
\ No newline at end of file