#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>

int arr(int*ar, int n)
{
	int sum = 0;
	for (int i = 0; i < n; i++) {
		sum = sum + ar[i];
	}
	return sum;
}

int main()
{
	int n;
	scanf("%d", &n);
	int *ar = (int*)malloc(n * sizeof(int));
	for (int i = 0; i < n; i++)
	{
		ar[i] = i * 2;
	}
	printf("%d", arr(ar, n));
	free(ar);
	return 0;
}