diff --git a/src/dollar.ts b/src/dollar.ts
index 2603133..25d57b9 100644
--- a/src/dollar.ts
+++ b/src/dollar.ts
@@ -1,9 +1,12 @@
 export class Dollar {
+  private tmpAmount: number
+
   constructor(public amount: number) {
+    this.tmpAmount = amount
     this.amount = amount
   }
 
   times(multiplier: number) {
-    this.amount *= multiplier
+    this.amount = this.tmpAmount * multiplier
   }
 }