#include <bits/stdc++.h>
#include <iostream>
#include <vector>
#include <algorithm>
#include <iomanip>
using namespace std;
typedef long long ll;

int main() {
	double t, s, d;
	cin >> t >> s >> d;
	double time = d / s;

	//ll day = time / 24;
	//double answer = day * 12;
	//time = fmod(time, 24);
	double answer = 0;
	while (true)
	{
		if (t >= 24)
		{
			t = 0;
		}
		if (time>=1)
		{
			time--;
			t += 1.0f;
			if (t<=5||19<=t)
			{
				answer++;
			}
		}
		else
		{
			if (t <= 5 || 18 <= t)
			{
				answer += time;
			}
			break;
		}
	}

	cout << std::setprecision(20) << answer << endl;
	return 0;
}