function Main(input) {
	input = input.split("\n");
	tmp = input[0].split(" ");
    let takahashiHP = Math.ceil(Number(tmp[0])/Number(tmp[3]))
    let aokiHP = Math.ceil(Number(tmp[2])/Number(tmp[1]))
  	if(takahashiHP >= aokiHP) return console.log('Yes')
    else return console.log('No')
}
Main(require("fs").readFileSync("/dev/stdin", "utf8"));
