Input power is also measured in kWs or watts, but it doesn't have anything to do with how well the aircon can cool your home. It does have to do with how much it will cost you to run it however.
The input power is how much electricity the aircon needs to run. The lower this number, the cheaper it is per hour to run the aircon. Ideally you want a device that has a low input wattage, and a high cooling capacity - this is measured as 'cooling efficiency'. Cooling efficiency refers to the how many watts of power is required to create one cooling unit. The greater that efficiency percentage, the better.
While it can be tempting to just look at the Energy Rating sticker, we would recommend against it. Most Australian consumer electronics are given a score between one, and six stars, although more recently these have gone up to ten! The more stars, the less energy that particular model will use.
Keep in mind however that these energy ratings are based on "how most people use their appliance" so there is no hard, and fast way of knowing if the kWh per year number is accurate for you. They're also comparitive between devices of similar size and features, so five stars on a 2.4Kw portable aircon isn't akin to five stars on a 7kW.