#include<stdio.h>

int main(void) {

	int a, b, c, d;

	scanf("%d %d %d %d", &a, &b, &c, &d);

	for (;;) {
		c -= b;
		if (c <= 0) {
			printf("Yes");
			break;
		}
		a -= d;
		if (a <= 0) {
			printf("No");
			break;
		}
	}
	return 0;
}