PRINT "Modular inverse."
    PRINT "What is the modulus?"
    INPUT M
    PRINT "What number is to be inverted?"
    INPUT X
    PRINT "Solution is:"
10  LET A = A + 1
    GOTO 20
15  IF B = 1 THEN PRINT A
    IF B = 1 THEN END
    IF A = M-1 THEN PRINT "nonexistent"
    IF A = M-1 THEN END
    GOTO 10
20  LET B = A*X
30  IF B < M THEN GOTO 15
    LET B = B - M
    GOTO 30