#include <iostream>
#include <cstring>
using namespace std;

double e;

bool done[222];
double dp[222];
double solve(int N){
    if(N == 0)return 0;
    if(done[N])return dp[N];
    
    double res = 0;
    for(int i=1;i<=6;i++){
        if(N - i < 0){
            res += e;
        } else {
            res += solve(N - i);
        }
    }
    
    res /= 6;
    res += 1;
    
    done[N] = true;
    return dp[N] = res;
}

int main(){
    int K;
    cin >> K;
    
    double lo = 0, hi = 1 << 30;
    for(int i=0;i<100;i++){
        e = (lo + hi) / 2;
        memset(done, false, sizeof(done));
    
        if(solve(K) < e){
            hi = e;
        } else {
            lo = e;
        }
    }
    
    printf("%.15f\n", lo);
    return 0;
}