#include <stdio.h>
#include <math.h>

int main(int argc, char const *argv[])
{
  unsigned int A, B, C, D;
  scanf("%u %u %u %u", &A, &B, &C, &D);

  int takahashi_turn = (int)ceil((float)C / B);
  int aoki_turn = (int)ceil((float)A / D);
  if (takahashi_turn <= aoki_turn)
  {
    printf("Yes");
  }
  else
  {
    printf("No");
  }
  return 0;
}
