If a 3rd argument is present and positive then
the calculation is done for periodic boundary conditions

First Argument: Number of Sites (mandatory)
Second Argument: TwiceS (optional, default to 1, that is s = 1/2)

Overrides Threads= in input line if present, and set threads
to number given here.

Say
Excited=5
and then you can measure with
./lanczos -f input.inp -m "<gs|n|P1>"
where |P1> is the first excited states.
The -m option is more general than shown, and is documented
elsewhere.

Say
Excited=5
to get the gs and the next 4 excited states.
This label is optional and defaults to 0 (which means g.s.)
Only energies are printed for now.