// cLayの乱数を取り出す方法はありますか？
mt19937_64 randdev(8901016);
inline ll rr(ll l, ll h) {
    return uniform_int_distribution<ll>(l, h)(randdev);
}

ll k;
ll sim(){
    int  c=0;
    for (int z=0;z!=k;z=k<(z+=rr(1,6))?0:z)++c;
    return c;
}

{
    rd(k);
    ll sm=0;
    rep(i,600000){sm+=sim();}
    printf("%.7f"(double)sm/600000);
}