#include <iostream>
#include <vector>
#include <algorithm>
#include <random>
using namespace std;

#define RREP(i,s,e) for (i = s; i >= e; i--)
#define rrep(i,n) RREP(i,n-1,0)
#define REP(i,s,e) for (i = s; i <= e; i++)
#define rep(i,n) REP(i,0,n-1)
#define INF 100000000

typedef long long ll;

int main() {
    int i, j, k;
    double dp[201];
    double l, r;
    cin >> k;
    l = 0; r = 1200;
    while (l+0.01 < r && l*1.01 < r) {
        double m = (l+r) / 2;
        dp[0] = 0;
        REP (i,1,k) {
            dp[i] = 0;
            REP (j,1,6) {
                if (i-j < 0)
                    dp[i] += m;
                else
                    dp[i] += dp[i-j];
            }
            dp[i] /= 6;
            dp[i]++;
        }
        if (dp[k] < m)
            r = m;
        else
            l = m;
    }
    cout << (r+l)/2 << endl;
    return 0;
}