#include <stdio.h>

int main() {
	int a, b, c, d;
	scanf("%d%d%d%d", &a, &b, &c, &d);
	int n;
	if (a % d == 0)n = a / d;
	else n = (a / d) + 1;
	//printf("%d", n);
	if (b * n >= c)printf("Yes");
	else printf("No");
	return 0;
}