Maybe this is not intended, but the provided binary prints "Access Granted" if the (incomplete) flag is partially correct:

```
import subprocess, string

def check(flag):
try:
output = subprocess.check_output('echo "%s" | ./main' % flag, shell = True, stderr=subprocess.STDOUT)
except Exception, e:
output = str(e.output)
return 'Access Granted' in output

flag = ''
for i in range(128):
for c in string.printable:
if check(flag + c):
flag += c
print flag
break
```