/*
yukicoder No.53
作成者：ヒロソフ
*/
#include <stdio.h>
double Calc(int k);
int main(void) {
	int N;
	scanf("%d", &N);
	printf("%.8f\n", Calc(N));
	return 0;
}
double Calc(int k) {
	if (k == 0) return 4;
	else if (k == 1) return 3;
	else return (19.0 * Calc(k - 1) - 12.0 * Calc(k - 2)) / 4.0;
}