#include<bits/stdc++.h>
typedef long long ll;
using namespace std;
int INF = 1e9;
int MOD = 1000000007;
main(){
    double dp[21];
    for(int i = 0;i <= 20;i++)dp[i] = 1;
    for(int i = 2;i <= 20;i++){
        for(int j = 1;j <= min(6,i-1);j++){
            dp[i] += dp[i-j] / 6.;
        }
    }
    int N;
    cin >> N;
    cout << dp[N] << endl;
}