program main
integer :: a,b,c,d

read(*,*) a,b,c,d

do while(a > 0 .and. c > 0)
c = c - b
if (c <= 0) exit 
a = a - d
end do

if (a > c) then 
write(*,*) "Yes"
else 
write(*,*) "No"
end if
end program main