import std.algorithm, std.array, std.container, std.range, std.bitmanip;
import std.numeric, std.math, std.bigint, std.random;
import std.string, std.conv, std.stdio, std.typecons;

void main()
{
  auto rd = readln.split.map!(to!int);
  auto h = rd[0], a = rd[1], d = rd[2];

  auto maxCa = h / a + (h % a == 0 ? 0 : 1);
  auto minE = h.to!real;
  foreach (ca; 0..maxCa + 1) {
    auto e = calc(h, a, d, ca);
    minE = min(minE, e);
  }

  writefln("%f", minE);
}

real calc(int h, int a, int d, int ca)
{
  h -= a * ca;
  auto e = ca.to!real;

  if (h > 0)
    e += (h / d + (h % d == 0 ? 0 : 1)).to!real * 3 / 2;

  return e;
}