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
#include
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