#include <bits/stdc++.h>
typedef  long long ll;
#define INF 1000000000
using namespace std;
#define MOD 1000000007
int main(void){
    double dp[21]={0};
    int k;
    cin>>k;
    dp[k]=0;
    for(int i=k-1;i>=0;i--){
        double sum=1;
        for(int j=1;j<=6;j++){
            int p=i+j;

            if(p>20){
                continue;
            }else{
                sum+=dp[p]*1/6;
            }
        }
        dp[i]=sum;
    }
    cout<<dp[0]<<endl;
}