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