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

#define REP(i, n) for(int i=0; i<(n); i++)
#define FOR(i, a, b) for(int i=(a);i<(b);i++)

int N;
signed main()
{
    cin >> N;
    printf("%.10f\n", 4.0 * pow(0.75, N));
    return 0;
}