#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)
#define FOR(i,b,e) for (int i=(int)(b); i<(int)(e); i++)
#define ALL(x) (x).begin(), (x).end()

const double PI = acos(-1);

int k;
double dp[32];

double dfs(int x) {
  if (x >= k) return 0.0;
  if (dp[x] != -1) return dp[x];
  double ret = 0;
  for (int i = 1; i <= 6; i++)
    ret += 1./6 * dfs(x + i);
  return dp[x] = ret + 1;
}

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

  REP (i, 32) dp[i] = -1;
  cin >> k;
  cout << fixed << setprecision(10) << dfs(0) << endl;
  
  return 0;
}