help me please ( students digree programe )

[mon4live]

my programe is a broblem

but i'll type to to u what i want to do ....

10 input "please enter your marks in x%",marks
if 0 < marks < 20 then
let digree = " bad "
if 21 < marks < 40 then
let digree = "not bad"
if 41 < marks < 60 then
let digree = "good"
if 61 < marks < 80
let digree = "very good"
if 81 < marks < 100 then
let digree = "exilleant"
end if
print "digree =";digree
goto 10

i hope u can help me ..... and thanks for your