#include "bits/stdc++.h"
using namespace std;
#define FOR(i,a,b) for(int i =(a);i<(b);i++)
#define REP(i,n) for(int i=0;i<(n);i++)
#define REPm(i,n) for(int i=(n)-1;i>=0;i--)
#define REP1(i,n) for(int i=1;i<=(n);i++)
#define mp make_pair
typedef long long ll;
double A[101];
int main(){
    int N;
    cin >> N;
    A[0] = 4.0;
    A[1] = 3.0;
    FOR(i,2,N+1){
        A[i] = (19*A[i-1]-12*A[i-2])/4.0;
    }
    printf("%.10f\n",A[N]);
    return 0;
}