#include <stdio.h>

int main() {

    int n = 0;
    scanf("%d", &n);//输入天数
    int a = 0;//带值所用
    int length = 0;//计算天数
    int total = 0;//计算金币总数
    while (n > length)
    {
        int i = 1000;//定义一个数字用于循环
        for (a = 1; a <= i; a++)
        {
            int j = 1;
            for (j = 1; j <= a; j++)
            {
                total += a;
                length++;

                if (length == n)
                {
                    break;
                }
            }
            if (length == n)
            {
                break;
            }
        } 
    }
    printf("%d\n", total);

    return 0;
}