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:

解题说明：水题一道，熟悉通项公式求和即可。

#include
#include
#include
#include
#include
#include
#include
using namespace std;

int main()
{
	int i,n,sum;
	scanf("%d",&n);
	sum=0;
	i=0;
	while(1)
	{
		i++;
		sum=i*(i+1)*(i+2)/6;
		if(sum>n)
		{
			break;
		}
	}
	printf("%d\n",i-1);
	return 0;
}