int main(void)
{
  int A, B, C, D;
  int flag = 0;
  int turn = 0;
  scanf("%d%d%d%d", &A, &B, &C, &D);
  while(flag == 0){
    if(turn % 2 == 0){
      C = C-B;
      turn = 1;
    }
    else{
      A = A-D;
      turn = 0;
    }
    if(A<=0 || C<=0)
      flag = 1;
  }
  
  if(A<=0)
    printf("No\n");
  if(C<=0)
    printf("Yes\n");
      
  return 0;
}