#include <bits/stdc++.h>

using namespace std;

int main(void) {
  int H, A, D;
  cin >> H >> A >> D;
  
  double ans = 1e9;
  for (int i = 0; i * A <= H; i++) {
    ans = min(ans, i + 1.5 * ((H - i * A + D - 1) / D));
  }
  printf("%.10f\n", ans);

  return 0;
}