diff --git a/stocks.js b/stocks.js
new file mode 100644
index 0000000..e6fbd36
--- /dev/null
+++ b/stocks.js
@@ -0,0 +1,38 @@
+/**
+ * After each day, consider the paper value of your portfolio.
+ * If you owned nothing yesterday, you can own 'a' or 'b' or nothing today.
+ * If you owned 'a' yesterday, you can own nothing or 'a' today.
+ * If you owned 'b' yesterday, you can own nothing or 'b' today.
+ *
+ * a1 = max(z0, a0 + pa1 - pa0)
+ * b1 = max(z0, b0 + pb1 - pa0)
+ * z1 = max(z0, a1, b1)
+ */
+var stocks1 = function (pa, pb) {
+    var a = 0, b = 0, z = 0;
+    for (var i = 1; i < pa.length; i++) {
+	a = Math.max(z, a - pa[i-1] + pa[i]);
+	b = Math.max(z, b - pb[i-1] + pb[i]);
+	z = Math.max(a, b);	
+    }
+    return z;
+}
+
+var stocks2 = function (pa, pb) {
+    var opta = [0];
+    var optb = [0];
+    var opt0 = [0];
+    for (var i = 1; i < pa.length; i++) {
+	opta[i] = Math.max(opt0[i-1], opta[i-1] - pa[i-1] + pa[i]);
+	optb[i] = Math.max(opt0[i-1], optb[i-1] - pb[i-1] + pb[i]);
+	opt0[i] = Math.max(opta[i], optb[i]);
+    }
+    return opt0[pa.length-1];
+}
+
+a = [2,8,1,2];
+b = [2,1,5,9];
+console.log(stocks1(a, b));
+console.log(stocksn(a, b))
+
+