# require "template"
lib C
  fun strtoll(s : UInt8*, p : UInt8**, b : Int32) : Int64
end

class String
  def to_i64
    C.strtoll(self, nil, 10)
  end
end

# require "graph"
struct Edge(T)
  property to : Int32
  property cost : T

  def initialize(@to : Int32, @cost : T)
  end
end

struct Edge2(T)
  property from : Int32
  property to : Int32
  property cost : T

  def initialize(@from : Int32, @to : Int32, @cost : T)
  end

  def reverse
    Edge2(T).new(to, from, cost)
  end
end

class Graph(T)
  getter size : Int32
  getter graph : Array(Array(Edge(T)))

  def initialize(@size : Int32)
    raise ArgumentError.new("Negative graph size: #{size}") unless size >= 0
    @graph = Array.new(size) { Array(Edge(T)).new }
  end

  def initialize(@size, edges : Array(Edge2(T)), undirected : Bool)
    raise ArgumentError.new("Negative graph size: #{size}") unless size >= 0
    @graph = Array.new(size) { Array(Edge(T)).new }
    edges.each do |edge|
      @graph[edge.from] << Edge.new(edge.to, edge.cost)
      @graph[edge.to] << Edge.new(edge.from, edge.cost) if undirected
    end
  end

  def add_edge(i : Int32, j : Int32, cost : T)
    raise IndexError.new unless 0 <= i < size
    raise IndexError.new unless 0 <= j < size
    graph[i] << Edge(T).new(j, cost)
    graph[j] << Edge(T).new(i, cost)
  end

  def add_edge_directed(i : Int32, j : Int32, cost : T)
    raise IndexError.new unless 0 <= i < size
    raise IndexError.new unless 0 <= j < size
    graph[i] << Edge(T).new(j, cost)
  end

  def [](i : Int32)
    graph[i]
  end

  def each_edge : Nil
    (0...size).each do |v|
      graph[v].each do |edge|
        yield Edge2(T).new(v, edge.to, edge.cost)
      end
    end
  end

  def edges : Array(Edge2(T))
    result = [] of Edge2(T)
    each_edge do |edge|
      result << edge
    end
    result
  end
end

# require "atcoder/PriorityQueue"
# ac-library.cr by hakatashi https://github.com/google/ac-library.cr
#
# Copyright 2021 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

module AtCoder
  # Implements standard priority queue like [std::priority_queue](https://en.cppreference.com/w/cpp/container/priority_queue).
  #
  # ```
  # q = AtCoder::PriorityQueue(Int64).new
  # q << 1_i64
  # q << 3_i64
  # q << 2_i64
  # q.pop # => 3
  # q.pop # => 2
  # q.pop # => 1
  # ```
  class PriorityQueue(T)
    getter heap : Array(T)

    def initialize
      initialize(&.itself)
    end

    # Initializes queue with the custom comperator.
    #
    # ```
    # q = AtCoder::PriorityQueue(Int64).new {|n| -n}
    # q << 1_i64
    # q << 3_i64
    # q << 2_i64
    # q.pop # => 1
    # q.pop # => 2
    # q.pop # => 3
    # ```
    def initialize(&block : T -> (Int8 | Int16 | Int32 | Int64 | UInt8 | UInt16 | UInt32 | UInt64))
      @heap = Array(T).new
      @priority_proc = block
    end

    # Pushes value into the queue.
    def push(v : T)
      @heap << v
      index = @heap.size - 1
      while index != 0
        parent = (index - 1) // 2
        if @priority_proc.call(@heap[parent]) >= @priority_proc.call(@heap[index])
          break
        end
        @heap[parent], @heap[index] = @heap[index], @heap[parent]
        index = parent
      end
    end

    # Alias of `push`
    def <<(v : T)
      push(v)
    end

    # Pops value from the queue.
    def pop
      if @heap.size == 0
        return nil
      end
      if @heap.size == 1
        return @heap.pop
      end
      ret = @heap.first
      @heap[0] = @heap.pop
      index = 0
      while index * 2 + 1 < @heap.size
        child = if index * 2 + 2 < @heap.size && @priority_proc.call(@heap[index * 2 + 1]) < @priority_proc.call(@heap[index * 2 + 2])
          index * 2 + 2
        else
          index * 2 + 1
        end
        if @priority_proc.call(@heap[index]) >= @priority_proc.call(@heap[child])
          break
        end
        @heap[child], @heap[index] = @heap[index], @heap[child]
        index = child
      end
      ret
    end

    # Returns `true` if the queue is empty.
    delegate :empty?, to: @heap

    # Returns size of the queue.
    delegate :size, to: @heap
  end
end


n, m = read_line.split.map(&.to_i)
a = read_line.split.map(&.to_i)
edges = (0...m).flat_map {
  u, v = read_line.split.map(&.to_i.pred)
  e = Edge2(Nil).new(u, v, nil)
  [e, e.reverse]
}
k = read_line.to_i
b = read_line.split.map(&.to_i.pred)

graph = Graph.new(n, edges.select { |e| a[e.from] < a[e.to] }, undirected: false)

count_in = [0] * n
graph.each_edge do |e|
  count_in[e.to] += 1
end

flag = [false] * n
b.each { |i| flag[i] = true }

que = Deque.new((0...n).select { |i| count_in[i] == 0 })
ans = [] of Int32
while v = que.shift?
  op = flag[v]
  if op
    flag[v] = false
    ans << v
  end
  graph[v].each do |e|
    count_in[e.to] -= 1
    flag[e.to] = !flag[e.to] if op
    que << e.to if count_in[e.to] == 0
  end
end

if flag.none?
  puts ans.size, ans.join('\n', &.succ)
else
  puts -1
end