#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); i++)
using namespace std;
using ll = long long;
using ld = long double;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(0);
    
    int H,A,D; cin >> H >> A >> D;
    ld ans = 1e18;
    for(int a = 0; a * A <= H + A; a++) {
        int R = H - a * A;
        ans = min(ans, ld(a + 1.5 * max(0, ((R + D - 1) / D))));
    }
    cout << ans << endl;
}