function Main(input) {
	tmp = input.split(" ");
	ts = parseInt(tmp[0], 10);
  ta = parseInt(tmp[1], 10);
	as = parseInt(tmp[2], 10);
  aa = parseInt(tmp[3], 10);
  for (i=1; ts > 0 && as > 0; i++) {
    if (i % 2 == 0) {
      ts = ts - aa
    } else {
      as = as - ta
    }
  }
  if (as <= 0) {
    console.log('Yes')
  } else {
    console.log('No')
  }
}
Main(require("fs").readFileSync("/dev/stdin", "utf8"));
