#include<stdio.h>
#include<stdlib.h>

void run(void){
  int k;
  scanf("%d",&k);
  double *now=(double *)malloc(sizeof(double)*(k+1));
  double *next=(double *)malloc(sizeof(double)*(k+1));

  int i,j;
  for(i=0;i<=k;i++){
    now[i]=0;
  }

  now[0]=1;
  double ans=0;
  for(i=1;i<=100000;i++){
    for(j=0;j<=k;j++){
      next[j]=0;
    }
    const double f=(double)1/6;
    for(j=0;j<k;j++){
      int n;
      for(n=1;n<=6;n++){
	next[(j+n>k)?0:(j+n)]+=f*now[j];
      }
    }
    ans+=i*next[k];
    next[k]=0;
    double *swap=now;
    now=next;
    next=swap;
  }
  printf("%lf\n",ans);
  return;
}

int main(void){
  run();
  return 0;
}