#include<stdio.h>

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