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