A9724. 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 $n$ ( $1<=n<=10^{4}$ ) — the number of cubes given to Vanya.

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

Illustration to the second sample: