#include <stdio.h>

int	main(void)
{
	int	A, B, C, D;

	scanf("%d %d %d %d", &A, &B, &C, &D);
	while (A > 0 && B > 0)
	{
		C -= B;
		if (C <= 0)
			break;
		A -= D;
	}
	if (A <= 0)
		printf("No\n");
	else if (C <= 0)
		printf("Yes\n");
	return (0);
}