|Codeforces Round #280 (Div. 2)|
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 ≤ 104) — the number of cubes given to Vanya.
Print the maximum possible height of the pyramid in the single line.
Illustration to the second sample: