100 A$ = "18446744073709551616"
 110 B$ = A$
 120 GOSUB 400
 130 PRINT E$
 140 END

 400  REM MULTIPLY A$ * B$
 410 C$ = "":D$ = "0"
 420  FOR I =  LEN (B$) TO 1 STEP  - 1
 430 C = 0:B =  VAL ( MID$ (B$,I,1))
 440  FOR J =  LEN (A$) TO 1 STEP  - 1
 450 V = B *  VAL ( MID$ (A$,J,1)) + C
 460 C =  INT (V / 10):V = V - C * 10
 470 C$ =  STR$ (V) + C$
 480  NEXT J
 490  IF C THEN C$ =  STR$ (C) + C$
 510  GOSUB 600"ADD C$ + D$
 520 D$ = E$:C$ = "0":J =  LEN (B$) - I
 530  IF J THEN J = J - 1:C$ = C$ + "0": GOTO 530
 550  NEXT I
 560  RETURN

 600  REM ADD C$ + D$
 610 E =  LEN (D$):E$ = "":C = 0
 620  FOR J =  LEN (C$) TO 1 STEP  - 1
 630  IF E THEN D =  VAL ( MID$ (D$,E,1))
 640 V =  VAL ( MID$ (C$,J,1)) + D + C
 650 C = V > 9:V = V - 10 * C
 660 E$ =  STR$ (V) + E$
 670  IF E THEN E = E - 1:D = 0
 680  NEXT J
 700  IF E THEN V =  VAL ( MID$ (D$,E,1)) + C:C = V > 9:V = V - 10 * C:E$ =  STR$ (V) + E$:E = E - 1: GOTO 700
 720  RETURN