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

int main()
{
	int ret;
	int A, B, C, D;
	ret = scanf("%d %d %d %d", &A, &B, &C, &D);

	do {
		/* takahashi */
		C -= B;
      if (C <= 0) break;
		/* aoki */
		A -= D;
	} while (A > 0 || C > 0);
	
	if (A > 0 && C <= 0)
		printf("Yes\n");
	else
		printf("No\n");
	
	fflush(stdout);
	return EXIT_SUCCESS;
}
