/*
yukicoder No.57
作成者：ヒロソフ
*/

#include <stdio.h>

int main(void) {
	double  base = 0;
	for (int i = 1; i <=6; i++)  base += i * 1.0 / 6.0;
	int dicenums;
	scanf("%d", &dicenums);
	printf("%f\n", base * dicenums);
	return 0;
}