function main(input) {
  const tmp = input.trim().split(' ')
  const a = parseInt(tmp[0], 10)
  const b = parseInt(tmp[1], 10)
  const c = parseInt(tmp[2], 10)
  const d = parseInt(tmp[3], 10)

  const ta = Math.ceil(c / b)
  const ao = Math.ceil(a / d)

  if (ta <= ao) {
    console.log('Yes')
  } else {
    console.log('No')
  }
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'))