#include<stdio.h>
void main()
{
	int A, B, C, D;
	scanf("%d %d %d %d", &A, &B, &C, &D);
	while (1)
	{
		C -= B;
		if (C <= 0)
		{
			printf("Yes");
			break;
		}
		A -= D;
		if (A <= 0)
		{
			printf("No");
			break;
		}
	}
}