#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
#else
  #define Debug(...) void(0)
#endif
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

int main() {
  int k;
  cin >> k;
  vector<double> dp(k + 6, 0);
  for (int i = k + 5; i >= 0; --i) {
    if (i >= k) dp[i] = 0;
    else {
      for (int j = 1; j <= 6; ++j) dp[i] += (dp[i + j] + 1) / 6;
    }
  }
  cout << fixed << setprecision(15) << dp[0] << endl;
  return 0;
}