program problemB
  implicit none


integer(8) :: n,m, yr, l, i, k, j,judge, small, kref, r, t, f, ref
integer(8) :: BNUM, RNUM, NMAX, count,MMAX, sum, A, B, C, D
character(len=4) :: color



read(*,*) A,B,C,D

if (B>=C) then
  write(*,*) 'Yes'
else
  if (int(real(A)/real(D))-real(A)/real(D)==0) then
    ref=int(real(A)/real(D))
  else
    ref=int(real(A)/real(D))+1
  end if
  if (int(real(C)/real(B))>ref) then
    write(*,*) 'No'
  else
    write(*,*) 'Yes'
  end if
end if


stop
end program
