#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <cctype>
#include <cmath>
#include <iostream>
#include <queue>
#include <list>
#include <map>
#include <numeric>
#include <set>
#include <sstream>
#include <string>
#include <vector>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;

int K;
map<int,double> memo;

double solve(int x){
  if(memo.count(x) > 0) return memo[x];
  if(x>=K) return 0.0;
  return memo[x] = 
    solve(x+1) * 1/6.0 +
      solve(x+2) * 1/6.0 +
        solve(x+3) * 1/6.0 +
          solve(x+4) * 1/6.0 +
            solve(x+5) * 1/6.0 +
              solve(x+6) * 1/6.0 +
                1.0;
}

int main(){
  cin >> K;
  printf("%.9lf\n", solve(0));
  return 0;
}