#include <algorithm>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <vector>
#define rep(i, n) for (int i = 0; i < (n); i++)
#define rrep(i, n) for (int i = (n)-1; i >= 0; i--)
#define pb push_back
#define all(a) (a).begin(), (a).end()
#define mp make_pair
using namespace std;
typedef long long int lli;
lli MOD = 1000000007;
double pos[300][210] = {};
int main()
{
    pos[0][0] = 1;
    int k;
    cin >> k;
    rep(i, 300) rep(j, k)
    {
        for (int l = 1; l <= 6; l++) {
            int a = l + j;
            if (a > k)
                a = 0;
            pos[i + 1][a] += 1.0 / 6.0 * pos[i][j];
        }
    }
    double ans = 0;
    rep(i, 300) ans += i * pos[i][k];
    printf("%.10f\n", ans);
}