#include <stdio.h>
#include<string.h>
int main (void){
int A,B,C,D;
scanf("%d%d%d%d",&A,&B,&C,&D);
if(A/D>C/B){
    printf("Yes");
}
else if(A/D==C/B){
    if(A%D!=0){
        printf("Yes");
    }else{
    printf("No");
}
}
        else if(A/D+1==C/B){
    if(C%B==0){
    printf("Yes");
    }else{
    printf("No");
}
}else{
    printf("No");
}
}
