#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>

int main(void) {
	int a, b, c, d;
	int p, q;
	scanf("%d %d %d %d", &a, &b, &c, &d);
	switch (c%b)
	{
		case 0:
			p = c / b;
			break;
		default:
			p = c / b + 1;
			break;
	}
	switch (a%d)
	{
		case 0:
			q = a / d;
			break;
		default:
			q = a / d + 1;
			break;
	}
	if (p <= q) puts("Yes");
	else puts("No");
	return 0;
}

