Okay, we know by conservation of energy that the input energy equals the output energy. That means QH, which means the energy input is equal to QC, the energy transferred into the cold body plus the work done by the system or by the molecules within the system. And this directly correlates the first law of thermodynamics. And in fact, it's the same thing. It's basically this. Okay, so we basically are saying that engines, heat engines aren't completely 100% efficient in converting heat into work.