#include <cassert>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <limits.h>
#include <map>
#include <queue>
#include <set>
#include <string.h>
#include <vector>

using namespace std;
typedef long long ll;

double TIME_LIMIT = 2.5;
ll startCycle;
const ll CYCLE_PER_SEC = 2700000000;

unsigned long long int getCycle() {
  unsigned int low, high;
  __asm__ volatile ("rdtsc" : "=a" (low), "=d" (high));
  return ((unsigned long long int) low) | ((unsigned long long int) high << 32);
}

double getTime(unsigned long long int begin_cycle) {
  return (double) (getCycle() - begin_cycle) / CYCLE_PER_SEC;
}

unsigned long long xor128() {
  static unsigned long long rx = 123456789, ry = 362436069, rz = 521288629, rw = 88675123;
  unsigned long long rt = (rx ^ (rx << 11));
  rx = ry;
  ry = rz;
  rz = rw;
  return (rw = (rw ^ (rw >> 19)) ^ (rt ^ (rt >> 8)));
}

int main() {
  int K;
  cin >> K;
  startCycle = getCycle();

  ll loop_cnt = 0;
  ll sum = 0;
  double currentTime = getTime(startCycle);

  while (currentTime < TIME_LIMIT) {
    int n = 0;
    ll cnt = 0;

    while (n < K) {
      n += (xor128() % 6) + 1;
      if (n > K) n = 0;
      ++cnt;
    }

    ++loop_cnt;
    sum += cnt;
    currentTime = getTime(startCycle);
  }

  cout << fixed << setprecision(10) << sum / (double) loop_cnt << endl;

  return 0;
}