The Rubik's CUBE is a 3-D mechanical puzzle invented in 1974 by Hungarian sculptor and professor of architecture Ernő Rubik. It is widely considered to be the world's best-selling toy, with over 350 million cubes sold worldwide. The CUBE consists of six faces, each of which is covered by nine stickers, among six solid colors. A pivot mechanism enables each face to turn independently, thus mixing up the colors. For the solution, each face must be returned to its original state. The Rubik's CUBE has been widely popular since its invention and is often referred to as the 'Rubik's CUBE' or simply 'the CUBE'.