2018/12/22 acm日常 第三周 CodeForces

B - Problem B

原题链接

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.

Examples
Input 1 Output 1
Input 25 Output 4

Note
Illustration to the second sample:

代码地址
思路：第一行1，第二行1+2，第x行1+2+…+x。
输入n个，则依次n-x，x则为自增（i+1），i也自增，就符合上述要求了。

#include<iostream>
using namespace std;
int main()
{
	int n;
	cin >> n;
	int i = 0, x = 1;
	for (;n>=x;)
	{
		i++;
		n -= x;
		x += i + 1;
	}
	cout << i << endl;
    return 0;
}