#include<stdio.h>

int main()
{
    int k = 0;
    int count = 0;
    int i = 0;
    int j = 0;
    int sum = 0;
    scanf("%d",&k);
    for (i = 1; i <= k; i++)
    {
        for (j = 0; j < i; j++)
        {
            sum += i;
            count++;
            if(k == count)//当count记录的每日金币结算次数和天数一样,则就可以停止了
            break;
        }
        if(k == count)//当count记录的每日金币结算次数和天数一样,则就可以停止了
        break;
    }
    printf("%d",sum);
    return 0;
}