Круговая диаграмма, ошибка "Система не поддерживает полноэкранный режим" - QBasic

INPUT n
DIM a(n)
CONST pi2 = 6.28318531#
proc1 = pi2 / 100
FOR i = 1 TO n
    INPUT a(i)
    s = s + a(i)
NEXT i
FOR i = 1 TO n
    a(i) = (a(i) * 100) / s
        PRINT a(i)
NEXT i
 
clr = 1
SCREEN 12
FOR i = 1 TO n
    clr = clr + 1
    st = st + (pi2 / 100) * a(i)
    DO WHILE u < st
        u = u + .01
        FOR j = 1 TO 50
            PSET (160 + SIN(u) * j, 100 - COS(u) * j), clr
        NEXT j
    LOOP
    COLOR clr
    PRINT a(i); "%"       
NEXT
COLOR 15