#include<bits/stdc++.h>
using namespace std;
#define fs first
#define sc second
#define pb push_back
#define mp make_pair
#define eb emplace_back
#define ALL(A) A.begin(),A.end()
#define RALL(A) A.rbegin(),A.rend()
typedef long long LL;
typedef pair<LL,LL> P;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
template<typename T> T gcd(T a,T b){return b?gcd(b,a%b):a;}
const LL mod=1000000007;
const LL LINF=1LL<<62;
const int INF=1<<30;
int dx[]={1,0,-1,0,1,-1,1,-1};
int dy[]={0,1,0,-1,1,-1,-1,1};



int main(){
    int h,a,d;cin >> h >> a >> d;
    vector<double> dp(h+1,INF);
    dp[h] = 0.0;
    double ans = INF;
    for (int i = h; i >= 0; i--) {
        if(i > d){
            chmin(dp[i - d], dp[i] + 3. / 2);
        }
        else{
            chmin(dp[0], dp[i] + 3. / 2);
        }
        chmin(ans, dp[i] + (i + a - 1) / a);
    }
    cout << setprecision(30) << fixed << ans << endl;
    return 0;
}