CodeForces 492A 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.

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.

input

1

output

1

input

25

output

4

Hint

Illustration to the second sample:



实现代码：

#include<iostream>
#include<cstdio>
using namespace std;
#define MAX 50
int num[MAX];
int main()
{
int  cube;
int sum=0;
scanf("%d",&cube);
num[1]=1;
for(int i=1;i<50;++i)
num[i]= (1+ i)*i/2;
for(int i=1;i<504;++i)
{
sum=sum+num[i+1];
if(sum>=cube)
{
printf("%d\n",i);
break;
}

}

return 0;

}

从提示可以看出 每层需要的方块为：(1+ i)*i/2