#include<stdio.h>
#include<stdlib.h>

int main(void) {
	int a, b, c, d;

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

	while (1) {
		c = c - b;
		if (c <= 0) {
			printf("Yes\n");
			return 0;
		}
		a = a - d;
		if (a <= 0) {
			printf("No\n");
			return 0;
		}
	}
}