#include <bits/stdc++.h>
using namespace std;
const int lim = 100;
double dp[lim];

int main(){
    int k;
    cin >> k;
    for(int i=1; i<lim; i++){
        for(int j=1; j<=min(6, i-1); j++){
            dp[i] += dp[i - j] / 6;
        }
        dp[i] += 1;
    }
    cout << fixed << setprecision(10) << dp[k] << endl;
}