#include <bits/stdc++.h>
using namespace std;

random_device rnd;

unsigned simulation(const int& K) {
    int cnt = 0, sum = 0;
    while (sum != K) {
        sum += rnd() % 6 + 1;
        if (sum > K) {
            sum = 0;
        }
        cnt++;
    }
    return cnt;
}

int main() {
    chrono::system_clock::time_point start, end;
    start = chrono::system_clock::now();
    int K;
    cin >> K;
    unsigned counter = 0;
    unsigned long long sum = 0;
    while (true) {
        end = chrono::system_clock::now();
        double time = static_cast<double>(chrono::duration_cast<chrono::microseconds>(end - start).count() / 1000.0);
        if (time > 1950) {
            break;
        }
        counter++;
        sum += simulation(K);
    }
    cout << (long double)sum / (long double)counter << endl;
}