const main = (input) => {
  const args = input.split(' ')
  let a = parseInt(args[0], 10)
  let b = parseInt(args[1], 10)
  let c = parseInt(args[2], 10)
  let d = parseInt(args[3], 10)

  while (1) {
    c = c - b
    if (c <= 0) {
      console.log('Yes')
      return
    }
    a = a - d
    if (a <= 0) {
      console.log('No')
      return
    }
  }
}

main(require('fs').readFileSync('/dev/stdin', 'utf8'))