#include <algorithm>
#include <iostream>

int main() {
    using namespace std;
    int h, a, d, ans = 100000;
    cin >> h >> a >> d;
    for (int i = 0; h + d >= 0; i++) {
        int j = (h > 0) ? (h + a - 1) / a : 0;
        h -= d;
        ans = min(ans, i * 3 + j * 2);
    }
    cout << ans / 2;
    if (ans % 2 == 1) { cout << ".5"; }
    cout << endl;
}