class Solve
  def initialize
    h, w, n = read_line.split.map(&.to_i)
    @xy = Array(Array(Int32)).new(n) { read_line.split.map(&.to_i.pred) }
    @graph = Array(Array({Int32, Int32})).new(h + w) { [] of {Int32, Int32} }
    @xy.each_with_index do |(x, y), i|
      @graph[x] << {h + y, i}
      @graph[h + y] << {x, i}
    end
    @cycle = [] of Int32
    @index = Array(Int32?).new(h + w, nil)
  end

  def dfs(v, p)
    if i = @index[v]
      ans = @cycle[i..]
      ans.rotate! if @xy[ans[0]][1] != @xy[ans[1]][1]
      puts ans.size, ans.join(' ', &.succ)
      exit
    end
    @index[v] = @cycle.size
    @graph[v].each do |u, i|
      next if u == p
      @cycle.push i
      dfs(u, v)
      @cycle.pop
    end
  end

  def solve
    @graph.size.times do |i|
      dfs(i, p) if @index[i].nil?
    end
    puts -1
  end
end

Solve.new.solve