'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]);
  const T = Math.ceil(hpA / attackT);
  const A = Math.ceil(hpT / attackA);

  if (T <= A) {
    console.log('Yes');
  } else {
    console.log('No');
  }
}

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