100 INPUT PROMPT "Number: ":N
120 PRINT MIDDLE$(N)
130 DEF MIDDLE$(N)
140   LET N$=STR$(ABS(N))
150   IF LEN(N$)<3 THEN LET MIDDLE$="Not enough digits":EXIT DEF
160   IF MOD(LEN(N$),2)=0 THEN LET MIDDLE$="Even number of digits":EXIT DEF
170   LET P=(LEN(N$)-3)/2
180   LET MIDDLE$=N$(P+1:P+3)
190 END DEF