#include <stdio.h>

int main() {
    int a;
    scanf("%d", &a);
    int sum = 0;
    int n = 1;
    while (a) {
        for (int i = 1; i <= n; i++) {
            if (a == 0)
                break;
            sum += n;
            a--;
        }
        n++;
    }
    printf("%d\n", sum);
    return 0;
}