#include <iostream>
#include <cstdio>
#include <algorithm>
using namespace std;

int main()
{
	int a,sum,day,mony,H,j;
	j = 1;
	sum = 0;
	mony = 0;
	day = 1;
	scanf("%d", &a);
	while(day <= a)
	{
		mony = mony + 1;
		j = 1;
		H = day;
		while(j<=H)
		{
			sum = sum + mony;
			day = day + 1;
			j = j + 1;
		}
	}
	printf("%d", sum);
}

卡住了，想不出来了，希望得到大佬的指点。。。