'use strict';
const p = s => console.log(s);

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

  while(1) {
    c -= b;
    a -= d;
    if(c <= 0) {
      p('Yes');
      break;
    }

    if(a <= 0) {
      p('No');
      break;
    }
  }
}
main(require('fs').readFileSync('/dev/stdin', 'utf8').trim().split("\n"));
