#include <stdio.h>
int main(void) {
  int A, B, C, D;
  scanf("%d %d %d %d", &A, &B, &C, &D);
  
  do{
    C=C-B;
    B=B-D;
  }while(C<0 ||B<0);
  
  if(C<0)
    printf("Yes");
  else
    printf("No");
  
  return 0;
}
