#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <cctype>
#include <cmath>
#include <iostream>
#include <queue>
#include <list>
#include <map>
#include <numeric>
#include <set>
#include <sstream>
#include <string>
#include <vector>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;

unsigned long long Comb(int n, int k){
  unsigned long long f[n+1][n+1];
  for(int i=0; i<n+1; i++) f[0][i] = f[i][0] = 1;
  for(int i=1; i<n+1; i++) for(int j=1; j<n+1; j++){
    f[i][j] = f[i-1][j]+f[i][j-1];
    if(i+j==n && j==k) return f[i][j];
  }
  return 1;
}

double calc(int B, int cnt){
  double ret = 0;
  for(int y=cnt;;){
    double sum = y * (double)Comb(y-1, cnt-1) * pow(1/3.0, y-cnt) * pow(2/3.0, cnt);
    if(sum < 10e-10) break;
    ret += sum;
    y++;
  }
  return ret;
}


int main(){
  int H, A, D;
  cin >> H >> A >> D;
  
  double ret = 1000000000.0;
  int x = 0;
  while(H-A*x>=0){
    int B = H-A*x;
    if(B==0){
      ret = min(ret, (double)x);
      break;
    }
    int cnt = B/D + ((B%D==0)?0:1);
    double y = calc(B, cnt);
    ret = min(ret, x+y);
    x++;
  }

  printf("%.6lf\n", ret);
  return 0;
}