function Main(input) {
    // 1行目がinput[0], 2行目がinput[1], …に入る
    var THP = input.split(' ')[0];
    var Tattack = input.split(' ')[1];
    var AHP = input.split(' ')[2];
    var Aattack = input.split(' ')[3];
    var count = 101;
    for (var i = 0; i < count; i++) {
        AHP = AHP - Tattack;
        if(AHP>0){
            THP = THP - Aattack;
            if (THP <= 0) {
                console.log("No");
                count = -1;
            }
        } else {
            count = -1;
            console.log("Yes");
        }
    }
}
Main(require("fs").readFileSync("/dev/stdin", "utf8"));