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

void run(void){

  int k;
  scanf("%d",&k);
  double c[206];
  double v[206];
  int i;
  for(i=k+1;i<=k+5;i++){
    c[i]=0.0;
    v[i]=1.0;
  }
  c[k]=v[k]=0.0;

  for(i=k-1;i>=0;i--){
    c[i]=1.0;
    v[i]=0.0;
    const double f=(double)1/6;
    int j;
    for(j=1;j<=6;j++){
      c[i]+=c[i+j]*f;
      v[i]+=v[i+j]*f;
    }
  }
  double ans=c[0]/(1.0-v[0]);
  printf("%.3lf\n",ans);
  return;
}

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