#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
// Yukicoder №65 回数の期待値の練習 ★★
// https://yukicoder.me/problems/no/365
// ***********************
// for debug
#define DEBUG
// -----------

#define NOP do{}while(0)
#ifdef DEBUG
#define TRACE(...) do{printf(__VA_ARGS__);fflush(stdout);}while(0)
#define TRACECR do{putchar_unlocked('\n');fflush(stdout);}while(0)
#else
#define TRACE(...) NOP
#define TRACECR NOP
#endif

#define	mypc(d)	putchar_unlocked((int)(d))
#define PRINCR mypc('\n')
#define NOCR(strig) do{char *p;p=strchr(strig,'\n');if(p)*p='\0';}while(0)
// The out-of-date function
#define	asctime(...)	asctime_s(...)
#define	ctime(...)		ctime_s(...)
#define	strlen(a)	mystr_len(a)

// for stdio
#define GETLINE(str) do{char *p;fgets(str,sizeof(str),stdin);p=strchr(str,'\n');if(p)*p='\0';}while(0)
#define mygc(c) (c)=getchar_unlocked()
static char *GETWORD(char* str) {char c;char *cp;cp=&str[0];mygc(c);while(c!=EOF){if((c==' ')||(c=='\n'))break;*cp++=c;mygc(c);}*cp='\0';return &str[0];}
#define	GETINTS(a,b) {char s[34];int *ap=a;REP(i,b){GETWORD(s);*ap++=atoi(s);}}
static int GETLINEINT(void) {char s[34];GETLINE(s);return atoi(s);}
static int GETWORDINT(void) {char s[34];GETWORD(s);return atoi(s);}
static long GETWORDLONG(void) {char s[34];GETWORD(s);return atol(s);}
static int maxi(int a,int b){if((a)>(b)){return a;}return b;}
static long maxl(long a,long b){if(a>b){return a;}return b;}
#define SWAP(type,a,b) do{type _c;_c=a;a=b;b=_c;}while(0)
#define REP(a,b) for(int a=0;a<(int)(b);++a)
#define REP1(a,b) for(int a=1;a<=(int)(b);++a)
#define Possible(a) 	   printf("%s",((a)?"Possible":"Impossible"))
#define possible(a) 	   printf("%s",((a)?"possible":"impossible"))

// *********************
// *********************
// *********************
int main( void ) {
	int	dice;
	double chance[20+12];

	REP(i,sizeof(chance)/sizeof(chance[0])) chance[i] = 0.;
	dice =GETWORDINT();

	while (dice--) {
		chance[dice] = 1.;
		REP1(i,6) chance[dice] += chance[ dice + i ] / 6.;
	}
	printf("%lf\n", chance[0]);
}