program day8
    implicit none
    integer, parameter :: max_chars = 400
    integer, parameter :: max_nodes = 1000
    integer, parameter :: max_iter = 100000
    character(200) :: fname
    character(max_chars) :: fline
    integer :: n_arguments
    integer :: istat
    character(max_chars) :: dir_ins
    integer :: n_dir_ins
    integer :: n_nodes
    character(len=3) :: node
    character(len=1) :: dir
    character(len=3) :: nodes(1:max_nodes), lnodes(1:max_nodes), rnodes(1:max_nodes)
    integer :: i, i2, cur, LRcur

    n_arguments = command_argument_count()
    if (n_arguments .eq. 1) then
        call get_command_argument(1, fname)
        print *, "File: ", trim(fname)
        print *
    else
        print *, "Wrong number of arguments: ", n_arguments
        stop
    end if

    open(10, file=fname)
    read(10, "(a)") dir_ins
    n_dir_ins = len_trim(dir_ins)
    read(10, "(a)") fline
    n_nodes = 0
    do i=1,max_nodes
        read(10, "(a)", iostat=istat) fline
        if ((len_trim(fline) .eq. 0) .or. (is_iostat_end(istat))) then
            exit
        end if
        read(fline(1:3), "(a)") nodes(i)
        read(fline(8:10), "(a)") lnodes(i)
        read(fline(13:15), "(a)") rnodes(i)
        n_nodes = n_nodes + 1
    end do
    close(10)
    cur = -1
    do i=1, n_nodes
        if (nodes(i) .eq. "AAA") then
            cur = i
            exit
        end if
    end do
    do i=1,max_iter
        LRcur = mod(i-1, n_dir_ins) + 1
        dir = dir_ins(LRcur:LRcur)
        if (dir .eq. "L") then
            node = lnodes(cur)
        else
            node = rnodes(cur)
        end if
        do i2=1, n_nodes
            if (nodes(i2) .eq. node) then
                cur = i2
                exit
            end if
        end do
        if (nodes(cur) .eq. "ZZZ") then
            exit
        end if
    end do
    if (nodes(cur) .eq. "ZZZ") then
        print *, "Found node ZZZ after ", i, " iterations"
    else
        print *, "Did not find node ZZZ after ", i, " iterations"
    end if

end program day8