#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <string>
#include <cmath>
#include <algorithm>
#include <vector>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <cstring>

typedef long long ll;
using namespace std;

#define mod 1000000009
#define INF 10000000
#define LLINF 2000000000000000000LL

#define SIZE 10001

int k;

double E(int x){
    if(k<=x) return 0;
    
    double ret=0;
    
    for(int i=1;i<=6;i++){
        ret+= E(x+i);
    }
    
    return ret/6.0+1;
}

int main(){
    scanf("%d",&k);
    
    printf("%.10lf\n",E(0));
    
    return 0;
}