#include <bits/stdc++.h>
typedef long long ll;
using namespace std;
#define DUMP(x)  cout << #x << " = " << (x) << endl;
#define FOR(i, m, n) for(ll i = m; i < n; i++)
#define IFOR(i, m, n) for(ll i = n - 1; i >= m; i-- )
#define REP(i, n) FOR(i,0,n)
#define IREP(i, n) IFOR(i,0,n)
#define FOREACH(x,a) for(auto& (x) : (a) )
#define ALL(v) (v).begin(), (v).end()
#define SZ(x) ll(x.size())

int main(){
  ll K; cin >> K;
  double lb = 0.0, ub = 1000, m ;
  //dp[i] = 総和がiの状態からスタートした場合の期待値
  vector<double> dp(K+6,0.0);
  //dp[0]を決め打ちして二分探索
  REP(_,100000){
    m = (lb+ub)/2.0;
    FOR(i,1,6) dp[K+i] = m;
    dp[K] = 0.0;
    IREP(i,K){
      dp[i] = 1.0;
      FOR(j,1,7) dp[i] += dp[i+j]/6.0;
    }
    if(m>dp[0]) ub = m;
    else lb = m;
  }
  cout << fixed << setprecision(10) << m << endl;
}