492A - Vanya and Cubes

A. Vanya and Cubes

time limit per test
1 second

memory limit per test
256 megabytes

input
standard input

output
standard output

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.

Input

The first line contains integer n (1 ≤ n ≤ 104)
— the number of cubes given to Vanya.

Output

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

Sample test(s)

input

1

output

1

input

25

output

4

Note

Illustration to the second sample:

n=gets.chomp.to_i
i,sum,count= 0,0,0
loop do
i += 1sum += i*(i+1)/2
break if sum>n
count += 1end
puts count