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.

题目大意：给个金字塔形。第一层1，第二层1+2，。。。。。。，第i层1+2+。。。+i，输入N，判断它最多能积累到哪一层。

解题思路：用等差数列的求和公式(1+i)*i/2求出每行的值，再用的变量将他们的值加到一起，在与N比较，看哪个数比N大，就说明N最多在I-1行。

代码：

 1 #include<iostream>
 2 #include<cstdio>
 3 using namespace std;
 4 int main()
 5 {
 6     int n,d=0,sum=0;
 7     while(cin>>n)
 8     {
 9         if(n>=1&&n<=10000)
10         {
11             int i=1;
12            while(1)
13            {
14                sum+=(1+i)*i/2;
15                if(sum>n)
16                {
17                    d=i-1;
18                    break;
19                }
20                i++;
21            }
22            printf("%d
",d);
23            d=0;
24         }
25     }
26     return 0;
27 }
28