#include <stdio.h>

int main() 
{
    int k=0,i=1,sum=0,count=1;
    scanf("%d",&k);
    while(k>0)
    {
        k=k-i;
        if(k>0)
        {
            sum+=count*i;
        }
        else 
        {
            sum+=(k+i)*count;
        }
        count++;
        i++;

    }
    printf("%d",sum);
    return 0;
}