rail, 412 bytes

Result

WA

Code [DL]

$'main'
 \---0(!x!)---\  
              |
/-------------/
|
|   /--s1(a)m----------------\
|   |                        o
|   \                        |
|    \              /-[1000]-/
\--1i----(!a!)(a)0q<
 /                  \
/                   |
|                   |
\                   |
 >-{~}-e(!x!)a(x)---/
/
|
\-(x)o#

$ '~' (a -- b):
 \
 |   /-t-\ #
 |  /     \|
 \-<       |
    \     /|
     \-f-/ @

stdin

6403470559113361629782910648073635164547016124432713216522872405000862646134414691987147750558089651

stdout

1000

stderr

Crash: Stack underflow

strace