program ABC164B
    implicit none
    integer(8)::A,B,C,D,flg
    read*,A,B,C,D
    flg=0
    do
        C=C-B
        if(C<=0)then
            flg=1
            exit
        end if
        A=A-D
        if(A<=0)exit
    end do

    if(flg==0)print'(A)',"No"
    if(flg==1)print'(A)',"Yes"
end program ABC164B