Даны три числа. Сумма каких двух чисел из них положительна — QBasic(Бейсик)

CLS
PRINT
PRINT "Nachojdenie dvych chisel iz trech,cumma kotorych polojitelna"
PRINT "Vvedite tri chisla"
INPUT "Pervoe...", a
INPUT "Vtoroe...", b
INPUT "Tret'e...", c
IF a = 0 AND b = 0 AND c = 0 THEN
PRINT "vse zadannye chisla ravny 0"
ELSE
IF a < 0 AND b < 0 AND c < 0 THEN
PRINT "vse zadannye chisla otrizatelnye"
ELSE
IF (a <= 0 AND b <= 0 AND c <= 0) THEN
PRINT "Zadannye chisla nepolojitelnye"
ELSE
d = a + b
e = a + c
f = b + c
IF d < 0 AND e < 0 AND f < 0 THEN PRINT "vse summy dvuh chisel otrizatelny"
IF d > 0 THEN PRINT "Summa pervogo i vtorogo chisel polojitelna."
IF e > 0 THEN PRINT "Summa pervogo i tretjego chisel polojitelna."
IF f > 0 THEN PRINT "Summa vtorogo i tretjego chisel polojitelna."
END IF
END IF
END IF