#include<bits/stdc++.h>

#define REP(i,s,n) for(int i=s;i<n;i++)
#define rep(i,n) REP(i,0,n)
#define EPS (1e-8)
#define equals(a,b) (fabs((a)-(b))<EPS)

using namespace std;

typedef vector<double> vd;
typedef vector<vd> mat;

vector<double> gauss_jordan(const mat& A,const vd& b){
  int n = A.size();
  mat B(n,vd(n+1));
  for(int i=0;i<n;i++) for(int j=0;j<n;j++) B[i][j] = A[i][j];

  for(int i=0;i<n;i++) B[i][n] = b[i];

  for(int i=0;i<n;i++) {
    int pivot = i;
    for(int j=i;j<n;j++) if( abs(B[j][i]) > abs(B[pivot][i]) ) pivot = j;
    swap(B[i],B[pivot]);
    if( abs(B[i][i]) < EPS ) return vd();
    
    for(int j=i+1;j<=n;j++) B[i][j] /= B[i][i];
    for(int j=0;j<n;j++) {
      if( i != j )  {
        for(int k=i+1;k<=n;k++) B[j][k] -= B[j][i] * B[i][k];
      }
    }
  }
  vd x(n);
  for(int i=0;i<n;i++) x[i] = B[i][n];
  return x;
}

int K;

void compute(){
  mat A(K+1,vector<double>(K+1,0));
  vd b(K+1,0);
  rep(src,K){
    REP(dst,src+1,src+7){
      if( dst <= K ) {
        A[src][dst] += -1;
      } else {
        A[src][0] +=  -( (src+7) - dst );
        break;
      }
    }
    A[src][src] += 6;
    b[src] += 6;
  }
  A[K][K] = 1;

  vector<double> answer = gauss_jordan(A,b);
  printf("%.10f\n",answer[0]);
}

int main(){
  cin >> K;
  compute();
  return 0;
}