#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000001

int main(){
	
	int H,A,D;
	cin>>H>>A>>D;
	double ans = 1e18;;
	rep(i,H+1){
		int remain = max(0,H - D * i);
		double temp = (remain+A-1)/A;
		temp += i * 1.5;
		ans = min(ans,temp);
	}
	
	cout<<fixed<<setprecision(10)<<ans<<endl;
	
	return 0;
}