function Main(input) {
    var [A,B,C,D] = input[0].split(" ").map(v=>v-0);
    while(A>0 && C>0){
        C-=B;
        if(C>0){
            A-=D;
        }
    }
    console.log(A>0?"Yes":"No")
}



Main(require("fs").readFileSync("/dev/stdin", "utf8").trim().split("\n"));