#include <stdio.h>

int main()
{
  int tB,tA,aB,aA,i;

  scanf("%d%d%d%d",&tB,&tA,&aB,&aA);

  while(1)
  {
    aB -= tA;
    if(aB <= 0)
      break;
    tB -= aA;
    if(tB <= 0)
      break;
  }

  if(aB <= 0)
    printf("Yes");
  else
    printf("No");

  return 0;
}
