#include<sstream>
#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<string>
#include<vector>
#include<set>
#include<map>
#include<queue>
#include<numeric>
#include<functional>
#include<algorithm>
#include<bitset>
using namespace std;
#define INF (1<<29)
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define all(v) v.begin(),v.end()
#define uniq(v) v.erase(unique(all(v)),v.end())
#define indexOf(v,x) (find(all(v),x)-v.begin())




int main(){
	int h,a,d;
	cin>>h>>a>>d;
	double ans=h;
	rep(i,h){
		int rem=max(0,h-i*a);
		int nd=(rem+d-1)/d;
		double e=i+nd*1.0/(2.0/3.0);
		ans=min(ans,e);
		if(h<i*a)break;
	}
	printf("%.2f\n",ans);
	return 0;
}