#include <stdio.h>

int main()
{
    int  h1, s1, h2, s2, i;
    scanf("%d %d %d %d", &h1, &s1, &h2, &s2);
    for (i=0; ; i++) {
        h2=h2-s1;
        h1=h1-s2;
        if (h2<=0 || h1<=0) break;
    }
    if (h2<=0) printf("Yes\n");
    else printf("No\n");
}
