#include<stdio.h>
int main(void){
    int a, b, c, d, x, y, z;
    scanf("%d%d%d%d",&a,&b,&c,&d);
    x=a/d;
    if(a%d!=0) x+=1;
    y=c/b;
    if(c%b!=0) y+=1;
    if(x==y) printf("Yes\n");
    else if(x>y) printf("Yes\n");
    else printf("No\n");
    return 0;
}