//HJ100 等差数列
#include <stdio.h>

int main(void) {
	int n = 0;
	while (~scanf("%d", &n)) {
		//等差求和：sn=n*a1+((n*(n-1)/2)*d
		printf("%d\n", n * 2 + ((n * (n - 1) / 2) * 3));
	}
	return 0;
}