#include<iostream>
#include<cstdio>
using namespace std;
int main(){
	int k,sm = 0,tmp = k,j = 1,l = 1;
	scanf("%d",&k);
	for(int i = 1; i <= k; i++){
		if(i <= tmp){
			sm += i * i;
			tmp -= i;
		}else{
			j = tmp;
			l = i;
			break;
		}
	}
	sm += j * l;
	printf("%d",sm);
	return 0;
}