"use strict";
function main(input) {
  let a = 0;
  let b = 0;
  let c = 0;
  let d = 0;
  [a,b,c,d] = input[0].trim().split(" ").map(i => parseInt(i));

  let ta = Math.floor(a/d) + ((a%d===0)?0:1);
  let tb = Math.floor(c/b) + ((c%b===0)?0:1);

  console.log((ta<tb)?"No":"Yes");
}
main(require('fs').readFileSync('/dev/stdin', 'utf8').trim().split("\n"));
