function min(a, b) {
  if (a > b) {
    return a
  }
  return b
}
function increase(id) {
  input = document.getElementById(id)
  step = parseFloat(input.step)
  input.value= min(parseFloat(input.value)+step, 0)
}
function decrease(id) {
  input = document.getElementById(id)
  step = parseFloat(input.step)
  input.value= min(parseFloat(input.value)-step, 0)
}