CF492A Vanya and Cubes

Vanya got $ n $ cubes. He decided to build a pyramid from them. Vanya wants to build the pyramid as follows: the top level of the pyramid must consist of $ 1 $ cube, the second level must consist of $ 1+2=3 $ cubes, the third level must have $ 1+2+3=6 $ cubes, and so on. Thus, the $ i $ -th level of the pyramid must have $ 1+2+...+(i-1)+i $ cubes. Vanya wants to know what is the maximum height of the pyramid that he can make using the given cubes.

The first line contains integer $ n $ ( $ 1

Print the maximum possible height of the pyramid in the single line.

Illustration to the second sample: