#include<cstdio>
#include<cstring>
#include<cctype>
#include<cmath>
#include<climits>
#include<algorithm>
#include<vector>
#include<valarray>
#include<string>
#include<set>
#include<map>
#include<stack>
#include<queue>
using namespace std;
  
  
#define rep(i,n) for(int i=0;i<n;i++)
#define REP(i,n) for(int i=1;i<=n;i++)
#define drep(i,n) for(int i=n-1;i>=0;i--)
#define DREP(i,n) for(int i=n;i>0;i--)
#define Rep(i,m,n) for(int i=m;i<n;i++)
#define scani(a) scanf("%d",&a)
#define scand(a) scanf("%lf",&a)
#define scans(s) scanf("%s",s)
#define printi(a) printf("%d",a)
#define prints(s) printf("%s",s)
#define LF printf("\n")
#define pb push_back
#define mp make_pair
#define bs binary_search
#define all(a) (a).begin(),(a).end()
#define MOD 100000007
  
typedef long long LL;
typedef vector<int> vi;
typedef vector<vector<int> > vvi;
typedef pair<double,double> pdd;
typedef pair<int,int> pii;
  
const double pi=acos(-1.0);
double rad(double t){return t*pi/180.0;}
  
int main(){
  int k;
  scani(k);
  valarray<double> E[210];
  E[0].resize(2);E[k+1].resize(2);
  E[0][0]=0.0;E[0][1]=0.0;
  E[k+1][0]=0.0;E[k+1][1]=1.0;
  for(int i=1;i<=k;i++){
    E[i].resize(2);
    E[i][0]=1.0;E[i][1]=0.0;
    for(int j=1;j<=6;j++){
      int t = i-j;
      if(t<0)t=k+1;
      E[i] += E[t]/6.0;
    }
  }

    printf("%.2lf\n",E[k][0]/(1.0-E[k][1]));
  return 0;
}