const main = input => {
  let n = input.split(' ').map(e => parseInt(e))
  
  let flag = 0
  while(n[0] > 0) {
    n[2] -= n[1]
    if(n[2] <= 0) {
      flag = 1
      break
    }
    n[0] -= n[3]
  }
  
  return flag == 1 ? "Yes" : "No"
}

console.log(main(require("fs").readFileSync("/dev/stdin", "utf8")))