program sample
implicit none
integer A,B,C,D
READ(*,*)A,B,C,D
10 CONTINUE
DO WHILE (C>0.OR.A>0)
C=C-B
If (C<=0) then
   WRITE(*,*) "NO"
END IF
A=A-D
IF(A<=0.AND.C>0) then
   WRITE(*,*) "YES"
END IF
END DO
stop
end program sample


