#define _USE_MATH_DEFINES
 
#include <iostream>
#include <iomanip>
#include <sstream>
 
#include <algorithm>
#include <cmath>
 
#include <string>
//#include <array>
#include <list>
#include <queue>
#include <vector>
#include <complex>
#include <set>
#include <map>
 
/////////
#define REP(i, x, n) for(int i = x; i < n; i++)
#define rep(i,n) REP(i,0,n)
#define P(p) cout<<(p)<<endl;
 
#define PII pair<int,int>
/////////
typedef long long LL;
typedef long double LD;
/////////
using namespace::std;
/////////

LD sumD[10001];

int main(void){
    std::cin.tie(0); 
    std::ios::sync_with_stdio(false);
    std::cout << std::fixed;//
    //cout << setprecision(16);//
	
	int H,A,D;
	cin>>H>>A>>D;

	for(int i=H-1;i>=0;--i){
		if(i+D >= H){
			sumD[i] = 1.5;
		}else{
			sumD[i] = sumD[i+D] + 1.5;
		}
	}
	int AllD = 0;
	//(H-AllD+A-1)/A
	//sumD[AllD]
	LD ans=10001,tans;
	for(int i=0;i<=(H+A-1)/A; ++i){
		tans = i+sumD[i*A];
		ans = min(ans,tans);
	}
	P(ans);
	return 0;
}