Expand import routine.

app/Support/Steam.php

@@ -284,6 +284,18 @@ class Steam
         return $amount;
     }
 
+    /**
+     * @param string $amount
+     *
+     * @return string
+     */
+    public function opposite(string $amount): string
+    {
+        $amount = bcmul($amount, '-1');
+
+        return $amount;
+    }
+
     /**
      * @param $string
      *