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

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int N; cin >> N;
    double dp[101];
    dp[0] = 4,dp[1] = 3;
    for(int i=2; i<=N; i++) dp[i] = dp[i-1]*4.75-dp[i-2]*3;
    
    cout << fixed << setprecision(20) << dp[N] << endl;
}