#include <stdio.h>

int main(void) {
	int A, B, C, D;
	int th, ta, ah, aa;
	if (scanf("%d%d%d%d", &A, &B, &C, &D) != 4) return 1;
	th = A;
	ta = B;
	ah = C;
	aa = D;
	for (;;) {
		ah -= ta;
		if (ah <= 0) {
			puts("Yes");
			return 0;
		}
		th -= aa;
		if (th <= 0) {
			puts("No");
			return 0;
		}
	}
}
