#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int (i) = 0 ; (i) < (int)(n) ; (i)++)
#define REP(i,a,b) for(int (i) = a ; (int)(i) <= (int)(b) ; (i)++)
#define all(n) (n).begin(),(n).end()
typedef long long ll;
typedef vector<int> Vi;
typedef vector<Vi> VVi;
typedef pair<long long,long long> Pii;
typedef vector<Pii> VPii;


int main(){
	int N;
	cin >> N;
	__float128 A[111];
	A[0] = 4;
	A[1] = 3;
	for(int i = 2 ; i <= N ; i++){
		A[i] = 19 / 4. * A[i-1] - 3. * A[i-2];
	}
	printf("%.15Lf",(long double)A[N]);
}