#include<bits/stdc++.h>
using namespace std;
int main()
{
	int n;//一共要发n天 
	cin>>n;
	int sum = 0;//计算总和，所有金币都加进去 
	int nowDay = 0;//当前发了几天 
	//第i轮 
	for(int i=1;;i++){
		//发i天，每天发i枚金币
		for(int j=1;j<=i;j++){
			sum+=i;//发出今天的金币 
			nowDay++;//已经发了的天数加一
			//如果已经发了 n 天了，停止这层循环 
			if(nowDay==n)
				break; 
		} 
		//如果已经发了n天了，停止这层循环 
		if(nowDay==n)
			break;
	} 
	cout<<sum<<"\n";

	return 0;
}

#include <bits/stdc++.h>
using namespace std;
int main()
{
    int day, nowDay, money;
    cin >> day;
    nowDay = money = 0;
    for (int i = 1;; i++)
    {
        // 发 i 天，每天 i 块钱
        for (int j = 1; j <= i; j++)
        {
            money += i;
            nowDay += 1;
            if (nowDay == day)
                break;
        }
        if (nowDay == day)
            break;
    }
    cout << money;
    return 0;
}