import java.io.*;

class Main{

static final PrintWriter out=new PrintWriter(System.out);

public static void main(String[] args) throws IOException{
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
String line="";
while((line=br.readLine())!=null&&!line.isEmpty()){
int n=Integer.parseInt(line);
double[] dp=new double[n+5];
dp[n-1]=1;
for(int i=n-2;i>=0;i--){
dp[i]=dp[i+1]/6+dp[i+2]/6+dp[i+3]/6+dp[i+4]/6+dp[i+5]/6+dp[i+6]/6+1;
}
out.printf("%.20f",dp[0]);
out.flush();
}
}
}