#include<stdio.h>
int main(void){
int A,B,C,D;

if(scanf("%d %d %d %d",&A,&B,&C,&D)!=0){
int x=(A+D-1)/D;
int y=(C+B-1)/B;
if(x>=y){
    printf("Yes\n");
}else{
    printf("No\n");
}
}else{
    printf("Failed to read integer.\n");
}
return 0;
}