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

int main(void)
{
  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;
    }
  }

  return 0;
}