The best way to do this type of thing is with some type of INPUT VALIDATION loop. Let me share simple demo for you:
HP = 0
DO
PRINT " A MONSTER APPEARD"
PRINT
PRINT "(1) GERMAN SUPLEX"
INPUT X
IF X <> 1 THEN PRINT "ERROR -- INVALID CHOICE"
LOOP UNTIL X = 1
IF X = 1 THEN HP = 0
DO.... LOOP UNTIL.... the input variable is in the proper range to be valid
HP = 0
DO
PRINT " A MONSTER APPEARD"
PRINT "(1) GERMAN SUPLEX"
INPUT X
IF X <> 1 THEN PRINT "ERROR -- INVALID CHOICE"
LOOP UNTIL X = 1
IF X = 1 THEN HP = 0
DO.... LOOP UNTIL.... the input variable is in the proper range to be valid