int main(void){
    int Thp,Tat,Ahp,Aat;

    scanf("%d%d%d%d",&Thp,&Tat,&Ahp,&Aat);
    while((Thp>0)&&(Ahp>0)){
        Ahp=Ahp-Tat;
        if(Ahp>0)
            Thp-=Aat;
    }
    if(Ahp<=0)
        printf("Yes\n");
    else
        printf("No\n");
    return 0;
}