const Main = (input) => {
  const tmp = input.split(' ')
  const takahashi = {
    hp: parseInt(tmp[0]),
    atk: parseInt(tmp[1]),
  }
  const aoki = {
    hp: parseInt(tmp[2]),
    atk: parseInt(tmp[3]),
  }
  let result = ''
  if (takahashi.hp / aoki.atk < aoki.hp / takahashi.atk) {
    result = 'no'
  } else {
    result = 'yes'
  }

  console.log(result)
}
Main(require('fs').readFileSync('/dev/stdin', 'utf8'))
