function Main(input) {
	input = input.split(" ");
	var tHP = parseInt(input[0], 10);
	var tAT = parseInt(input[1], 10);
	var aHP = parseInt(input[2], 10);
	var aAT = parseInt(input[3], 10);


var a =  Math.ceil(aHP  /  tAT )

var t =  Math.ceil(tHP  /  aAT )

if (t >= a){
	console.log('Yes');
}else{
	console.log('No');

}


}

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