#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
const int INF = 1000000000;
#define REP(i,s,n) for(int i=(int)(s);i<(int)(n);i++)
#define rep(i,n) REP(i, 0, n)
int K;
double memo[100];
double dfs(int x){
    double& res = memo[x];
    if(res != -1.0) return res;
    if(x >= K) return res = 0.0;
    res = 1.0;
    REP(i, 1, 7) res += dfs(x + i) / 6.0;
    return res;
}
int main(){
    cin >> K;
    rep(i, 100) memo[i] = -1.0;
    cout << fixed << setprecision(10) << dfs(0) << endl;;
    return 0;
}