#include<iostream>
using namespace std;

int main()
{
    int k,i,j,s1=0,s2=0;
    cin>>k; 
    for(i=1;;i++)
    {
    s1+=i;
    if(s1>=k)
    break;
    }
    for(j=1;j<=i-1;j++)
      s2+=j*j;
    s2+=i*(k-(s1-i));
    return 0;
     //s2=1*1+2*2+3*3
     //s2+=4*(8-(10-4))
 } ```