Fly me to ... mars (in just 3 months)

''Dreamed up in 1929 by Hermann Oberth, one of the fathers of rocket science, the technique relies on the simple fact that faster-moving objects have more energy than slower ones. So, let's say you're in a spaceship at a fueling station in Earth orbit, near the moon: First you thrust back toward the planet (burn number one), where the force of gravity accelerates the craft. Then you point yourself in the right direction and punch the rockets again (burn number two).'' [source]