#include <stdio.h>
int main()
{
	int a, b, c, d;
	int at=0, tt=0;
	scanf("%d%d%d%d", &a, &b, &c, &d);

	while (a > 0) {
		a = a - d;
		tt++;
	}
	while (c > 0) {
		c = c - b;
		at++;
	}

	if (tt >= at)
		printf("Yes\n");
	else
		printf("No\n");

	return 0;
}