#include "bits/stdc++.h"
using namespace std;

typedef long long Int;
#define REP(i,n) for(int (i)=0;(i)<(int)(n);++(i))

long double A[101];
int main() {
	A[0] = 4;
	A[1] = 3;
	for (int i = 2; i <= 100; i++) {
		A[i] = (19 * A[i - 1] - 12 * A[i - 2] ) / 4;
 	}
	int n; cin >> n;
	printf("%.22f\n", A[n]);
}