#include <stdio.h>

main()
{
	int a, b, c, d;
	int p, q;

	scanf("%d %d %d %d", &a, &b, &c, &d);
	p = (a + c - 1) / c;
	q = (b + d - 1) / d;
	if(p >= q) {
		printf("Yes");
	} else {
		printf("No");
	}
}