#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <string>
#include <vector>
#define rep(x,to) for(int (x)=0;(x)<(to);(x)++)

using namespace std;


int main()
{

	int k; cin >>k;
	
	double p[2][220]={}, res=0;
	p[0][0]=1.0;
	rep(i,50000){
		int cur=i&1,  nxt=cur^1;
		rep(j,220) p[nxt][j]=0.0;
		rep(j,k) rep(s,6){
			if(j+ s+1 <=k) p[nxt][j+s+1] += p[cur][j] /6.0;
			else p[nxt][0] += p[cur][j] /6.0;
		}
		res += (i+1) * p[nxt][k]; 
	}
	printf("%.10f", res);
	return 0;
}