Fifteen - a puzzle, which is a 15 square tiles. All knuckles are enclosed in a 4x4 square (the side of the square is four times longer than the knuckles). Thus, when you place the knuckles in the square, there is one empty space about the size of one knuckle that can be used to move the knuckles. The goal of the game is to arrange the placement of numbers by placing them in ascending order from left to right and from top to bottom, starting with the knuckles with the number 1 in the upper left corner and ending with the empty space in the lower right corner. You can share your result in social networks, by e-mail, etc. Play with your friends, relatives, co-workers, acquaintances, etc. Mix the knuckles in places and ask others to assemble them. Good luck !!!