#include<stdio.h>
int main()
{
    double p1, s1, p2, s2;
    int x, y;
    scanf("%lf %lf %lf %lf", &p1, &s1, &p2, &s2);
    x = ceil(p2/s1);
    y = ceil(p1/s2);
    if(x<=y){
        printf("Yes\n");
    }
    else printf("No\n");

    return 0;
}
