#include <bits/stdc++.h>

using namespace std;

double mean(int k) {
  vector<double> dp(k);
  for (int i = k-1; i >= 0; i--) {
    dp[i] = 1;
    for (int j = 1; j <= 6; j++) {
      dp[i] += 1.0 / 6 * (i + j < k ? dp[i+j] : 0);
    }
  }
  return dp[0];
}

double pos(int k) {
  vector<vector<double> > dp(k + 1, vector<double>(k + 6));
  dp[0][0] = 1.0;

  for (int i = 0; i < k; i++) {
    for (int j = 0; j < k; j++) {
      for (int l = 1; l <= 6; l++)
        dp[i+1][j+l] += dp[i][j] / 6;
    }
  }

  double ret = 0;
  for (int i = 0; i <= k; i++)
    ret += dp[i][k];
  return ret;
}

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  int k;
  cin >> k;

  double m = mean(k);
  double p = pos(k);
  cout << fixed << setprecision(12) << m / p << endl;
  
  return 0;
}