local k, a, b = io.read("*n", "*n", "*n")
if k <= a then
  print(1)
elseif a <= b then
  print(-1)
else
  if (k - a) % (a - b) == 0 then
    print((k - a) // (a - b) * 2 + 1)
  else
    print((k - a) // (a - b) * 2 + 3)
  end
end