#include <stdio.h>

int main() {
    int coin = 0;
    int day = 0;
    int i = 0;
    int K = 0;
    scanf("%d", &K);
    for (i = 1; day + i <= K;day += i,i++)
    {
        coin += i*i;
    }
    if (day != K&&day < K)
    {
        coin = coin + (K - day) * i;
    }
    printf("%d", coin);
    return 0;
}