#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;
long double B[101];
int main(){
    int N;
    cin >> N;
    B[0] = 4;
    B[1] = 12;
    FOR(i,2,N+1){
        B[i] = 19*B[i-1]-48*B[i-2];
    }
    B[N] /= pow(4.0,N);
    printf("%.10Lf\n",B[N]);
    return 0;
}