#include <bits/stdc++.h>

using namespace std;

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()

template<typename A, typename B> inline bool chmax(A &a, B b) { if (a<b) { a=b; return 1; } return 0; }
template<typename A, typename B> inline bool chmin(A &a, B b) { if (a>b) { a=b; return 1; } return 0; }

typedef unsigned long long ull;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<int, pii> P;

const ll INF = 1ll<<29;
const ll MOD = 1000000007;
const double EPS  = 1e-10;

double dp[10001];
int h, a, d;

int main() {
	cin >> h >> a >> d;
	
	fill(dp, dp + h + 1, INF);
	dp[0] = 0;
	
	FOR(i, 1, h + 1) {
		if (i <= a) dp[i] = 1;
		else chmin(dp[i], dp[i - a] + 1);
		
		int diff = d;
		while (i - diff >= -d) {
			double cnt = ceil(diff / d) * 1.5;
			
			if (i - diff < 0) chmin(dp[i], cnt);
			else chmin(dp[i], dp[i - diff] + cnt);
			
			diff += d;
		}
	}
	
	printf("%.15f\n", dp[h]);
	
	return 0;
}