READ(input, cell1, 0)

IF input % 2 == 0 THEN
    prime = false
ELSE
    FOR k = 3 TO SQRT(input) STEP 2
        IF input % k == 0 THEN
            prime = false
            GOTO exit
        END IF
    NEXT k
    prime = true
END IF
exit:
    WRITE(prime, cell1, 1)