Solution 2a aborts when compiled with PETSc

Solution 2a when built with PETSc sigaborts.
Backtrace is

```log
At line 83 of file inoutproc/Problem.f90 (unit = 101, file = 'input.in')
Fortran runtime error: Bad real number in item 1 of list input

Error termination. Backtrace:
#0 0x7f5115990533 in read_real
at ../../../../gcc-12.1.0/libgfortran/io/list_read.c:2025
#1 0x7f51159918dd in list_formatted_read_scalar
at ../../../../gcc-12.1.0/libgfortran/io/list_read.c:2179
#2 0x407035 in ???
#3 0x40dd15 in ???
#4 0x40e157 in ???
#5 0x7f511536b082 in __libc_start_main
at ../csu/libc-start.c:308
#6 0x40248d in ???
#7 0xffffffffffffffff in ???
```

## Compilation instructions

On the main branch
```sh
cd solutions/2a
make -C src petsc
```

The current `makefile` however is not entirely correct on how to include/link to PETSc you have to replace the section of the `makefile`
with the following to compile and set `PETSC_DIR` and `PETSC_ARCH` as well as your `LD_LIBRARY_PATH`

```sh
export PETSC_DIR=~/Programs/petsc-tmp && export PETSC_ARCH=recode && export LD_LIBRARY_PATH=${PETSC_DIR}/${PETSC_ARCH}:${LD_LIBRARY_PATH}
```

```makefile
#- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
# PETSc
#- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
PETSC_INC_PATH = -I$(PETSC_DIR)/include -I$(PETSC_DIR)/$(PETSC_ARCH)/include
PETSC_LINK_PATH = -L$(PETSC_DIR)/lib -L$(PETSC_DIR)/$(PETSC_ARCH)/lib
PETSC_LOAD_PATH = -Wl,-rpath=$(PETSC_DIR)/$(PETSC_ARCH)/lib
PETSC_LIBS = -lpetsc
```

**There is no need to fix the makefile in main since it will be replaced with CMake.** I have already written the CMake file I am just ironing out some compilation bugs with CMake + PETSc and examples `1b` and `2b`

Reproduce the issue from solutions/2a using make -C src petsc and the PETSc environment described in the report. Inspect inoutproc/Problem.f90 around line 83 and the in-progress CMake configuration; done means Solution 2a builds and runs with PETSc without the reported input parsing abort.

Written by the indexing model from the issue text.