#include <iostream>
#include <vector>
#include <limits>
#include <algorithm>
#include <iomanip>

using namespace std;

int main() {
	int h, a, d;
	cin >> h >> a >> d;
	vector<double> specialCounts(h + 1);
	specialCounts[0] = 0;
	for (int i = 1; i <= h; ++i) {
		specialCounts[i] = 0;
		if (i >= d) {
			specialCounts[i] += specialCounts[i - d];
		}
		specialCounts[i] += 3. / 2.;
	}
	double minTotalCount = numeric_limits<double>::max();
	for (int normalCount = 0; normalCount <= (h + a - 1) / a; ++normalCount) {
		int remaining = max(0, h - a * normalCount);
		double totalCount = (double)normalCount + specialCounts[remaining];
		minTotalCount = min(minTotalCount, totalCount);
	}
	cout << fixed << setprecision(4) << minTotalCount << endl;
	return 0;
}