function Main(input) {
	var str = input;
	str = str.split("\n")[0];
    str = str.split(' ');
    var thp = Number(str[0]);
    var tpw = Number(str[1]);
    var ahp = Number(str[2]);
    var apw = Number(str[3]);
    while(thp > 0 && ahp > 0 ){
   		ahp = ahp - tpw;
   		if(ahp <=0){
   			console.log("Yes");
   			break;
   		}
   		thp = thp - apw;
   		if(thp <=0){
   			console.log("No");
   			break;
   		}
    }
}
 //*おまじない
Main(require("fs").readFileSync("/dev/stdin", "utf8"));
