#include <stdio.h>
int a, b, c, d, e;
int main() {
	scanf("%d%d%d%d", &a, &b, &c, &d);
	while (a > 0 && c > 0) {
		if (e)a -= d;
		else c -= b;
		e = 1 - e;
	}
	if (a <= 0)printf("No\n");
	else printf("Yes\n");
}