#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define REP(i, n)           for(int(i)=0;(i)<(n);++(i))
#define RREP(i, n)          for(int(i)=(n)-1;(i)>=0;--(i))

double solve(int i){
    if(i <= 0) return 0.0;
    if(i == 1) return 1.0;
    double result = 0;
    for(int j = 1; j <= 6; j++){
        result += solve(i-j) * 1.0/6;
    }
    return result+1;
}

int main(){
    int N;
    cin >> N;
    cout << fixed << setprecision(9) << solve(N) << endl;
    return 0;
}