#include <iostream>
using namespace std;

int main() {
    int t, s, d;
    cin >> t >> s >> d;

    double time_to_drive = (double)d / s;
    double time_to_drive_carefully = time_to_drive;
    if (t <= 6 || t + time_to_drive >= 18) {
        time_to_drive_carefully += ((t + time_to_drive >= 18) ? 18 - t - time_to_drive : 6 - t);
    }

    cout << time_to_drive_carefully << endl;

    return 0;
}