'use strict';

function main(input) {
  const arr = input.trim().split(' ');
  const hpT = Number(arr[0]);
  const attackT = Number(arr[1]);
  const hpA = Number(arr[2]);
  const attackA = Number(arr[3]);
  let loseT = false;
  let loseA = false;

  for (let i = 0; i < 1000; i++) {
    hpA -= attackT;
    if (hpA <= 0) {
      return loseA = true;
    }
    haT -= attackA;
    if (hpT <= 0) {
      return loseT = true;
    }
  }

  if (loseT) {
    console.log('No');
  } else if (loseA) {
    console.log('Yes');
  }
}

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