class Heap
	require 'forwardable'
	extend Forwardable

	def initialize
		@array = []
		@index = {}
	end

	def add(obj, key)
		@array << [obj, key]
		@index[obj] = @array.size - 1
		lift_up(@array.size - 1)
	end

	def swap(i, j)
		u = @array[i]
		v = @array[j]
		@index[u[0]], @index[v[0]] = j, i
		@array[i], @array[j] = v, u
	end

	def lift_up(i)
		return if i == 0
		j = (i - 1) / 2
		if (@array[i][1] <=> @array[j][1]) < 0
			swap(i, j)
			lift_up(j)
		end
	end

	def del_min
		raise "heap is empty!" if empty?
		min = @array[0]
		if size > 1
			swap(0, @array.size-1)
			@array.pop
			lift_down(0)
		else
			@array.pop
		end
		@index.delete(min[0])
		min
	end

	def inc_key(obj, diff)
		i = @index[obj]
		@array[i][1] += diff
		lift_down(i)
	end

	def dec_key(obj, diff)
		i = @index[obj]
		@array[i][1] -= diff
		lift_up(i)
	end

	def update_key(obj, new_key)
		i = @index[obj]
		return unless i
		return if (new_key <=> @array[i][1]) >= 0
		@array[i][1] = new_key
		lift_up(i)
	end

	def min_obj
		@array[0][0]
	end

	def min_key
		@array[0][1]
	end

	def lift_down(i)
		j = 2 * i + 1
		k = j + 1
		if k >= size
			return if j >= size
			if (@array[i][1] <=> @array[j][1]) > 0
				swap(i, j)
				lift_down(j)
			end
		else
			l = ((@array[j][1] <=> @array[k][1]) < 0 ? j : k)
			if (@array[i][1] <=> @array[l][1]) > 0
				swap(i, l)
				lift_down(l)
			end
		end
	end

	def_delegators :@array, :empty?, :size
end

module Graphical
	require 'set'

	def get_path_by_bfs(s, t)
		prev_node = {}
		reached = Set[s]
		queue = [s]
		while !queue.empty? 
			u = queue.shift
			each_out_connection_of(u){|v, _|
				next if reached.include?(v)	
				reached << v
				queue << v
				prev_node[v] = u

				if v == t
					path = [v]
					while v = prev_node[v]
						path.unshift v
					end
					return path
				end
			}
		end	
		return nil
	end

	def get_path_by_dfs(s, t, reached = Set.new)
		reached << s
		return [s] if s == t
		each_out_connection_of(s){|v|
			next if reached.include?(v)
			path = get_path_by_dfs(v, t, reached) 
			return [s] + path if path
		}
		nil
	end

	def reachable_from(s, max_depth = nil)
		reached = Set[s]
		queue = [s]
		depth = 0
		loop {
			break if max_depth && depth >= max_depth
			next_queue = []
			until queue.empty?
				u = queue.shift
				each_out_connection_of(u){|v, _|
					next if reached.include?(v)
					reached << v
					next_queue << v
				}
			end
			break if next_queue.empty?
			queue = next_queue
			depth += 1
		}
		return reached
	end

	def bfs(start)
		raise "start must be Enumerable" if !start.kind_of?(Enumerable)
		reached = Set[*start.to_a]
		queue = []
		start.each{|s| queue << s}
		dist = {}
		loop.with_index {|_, depth|
			next_queue = []
			until queue.empty?
				u = queue.shift
				return depth if block_given? && yield(u, depth)
				dist[u] = depth
				each_out_connection_of(u){|v, _|
					next if reached.include?(v)
					reached << v
					next_queue << v
				}
			end
			break if next_queue.empty?
			queue = next_queue
		}
		block_given? ? nil : dist
	end

	def dijkstra(start)
		raise "start must be Enumerable" if !start.kind_of?(Enumerable)
		h = Heap.new
		reached = Set[*start.to_a]
		start.each{|s| h.add(s, 0)}

		dist = {}
		until h.empty?
			u, key = h.del_min
			return key if block_given? && yield(u, key)
			dist[u] = key
			each_out_connection_of(u){|v, l|
				d = dist[u] + l
				if reached.include?(v)
					h.update_key(v, d)
				else
					h.add(v, d)
					reached << v
				end
			}
		end
		block_given? ? nil : dist
	end

	def bidir_dijkstra(s, t)
		f_dist = {}
		b_dist = {}

		f_heap = Heap.new
		b_heap = Heap.new

		f_heap.add(s, 0)
		b_heap.add(t, 0)

		f_reached = Set[s]
		b_reached = Set[t]

		f_current_dist = b_current_dist = 0
		best = Float::INFINITY

		loop {
			if !f_heap.empty?
				u, key = f_heap.del_min
				f_dist[u] = key
				f_current_dist = key
				each_out_connection_of(u){|v, l|
					d = f_dist[u] + l
					if b_dist[v]
						path_len = d + b_dist[v]
						best = path_len if path_len < best
					end
					if f_reached.include?(v)
						f_heap.update_key(v, d)
					else
						f_heap.add(v, d)
						f_reached << v
					end
				}
			end

			if !b_heap.empty?
				u, key = b_heap.del_min
				b_dist[u] = key
				b_current_dist = key
				each_in_connection_of(u){|v, l|
					d = b_dist[u] + l
					if f_dist[v]
						path_len = d + f_dist[v]
						best = path_len if path_len < best
					end
					if b_reached.include?(v)
						b_heap.update_key(v, d)
					else
						b_heap.add(v, d)
						b_reached << v
					end
				}
			end

			return best if f_current_dist + b_current_dist >= best
			return nil if f_heap.empty? && b_heap.empty?
		}
	end

	def a_star(start)
		raise "a_star need termination condition" unless block_given?
		h = Heap.new
		reached = Set[start]
		h.add(start, [a_star_heuristic(start), 0])

		dist = {}
		until h.empty?
			u, (e, d) = h.del_min
			return d if yield(u, dist)
			dist[u] = d
			each_out_connection_of(u){|v, l|
				d = dist[u] + l
				e = d + a_star_heuristic(v)
				if reached.include?(v)
					h.update_key(v, [e, d])
				else
					h.add(v, [e, d])
					reached << v
				end
			}
		end
		block_given? ? nil : dist
	end

	def prim(start)
		h = Heap.new
		h.add(start, 0)
		reached = Set[start]
		tree_len = 0

		until h.empty?
			u, key = h.del_min
			tree_len += key

			each_out_connection_of(u){|v, d|
				if reached.include?(v)
					h.update_key(v, d)
				else
					h.add(v, d)
					reached << v
				end
			}
		end
		tree_len
	end

	def each_layer_from(start)
		raise "start must be Enumerable" if !start.kind_of?(Enumerable)
		return enum_for(__method__, start) unless block_given?
		reached = Set[*start]
		current_layer = start

		loop {
			yield current_layer
			next_layer = []
			current_layer.each{|u|
				each_out_connection_of(u){|v|
					next if reached.include?(v)
					reached << v
					next_layer << v
				}
			}	

			return if next_layer.empty?
			current_layer = next_layer
		}
	end
end

class Graph
	include Graphical

	def initialize(*options)
		@options = Set[*options]
	end

	def add_node(property = {})
		Node.new(property)
	end

	def add_edge(u, v, property = {})
		e = Edge.new(u, v, property)
		u.add_edge(e)
		v.add_edge(e)
		e
	end
	
	def del_edge(e)
		u, v = e.opposite.keys
		u.del_edge(e)
		v.del_edge(e)
		e
	end

	class Node
		def initialize(property)
			@property = property
			@edges = Set.new
		end

		def add_edge(e)
			@edges << e
		end

		def del_edge(e)
			@edges.delete(e)
		end

		def to_s
			@property[:name] || super
		end

		def each_edge
			@edges.each{|e| 
				yield e
			}
		end

		attr_reader :property
	end

	class Edge
		def initialize(u, v, property)
			@opposite = {u => v, v => u}
			@property = property
		end
		attr_reader :opposite, :property

		def to_s
			@property[:name] || super
		end

		def length
			@property[:length] || 1
		end

		def actual_capacity(from)
			v = @opposite[from]
			cap = @property[:capacity]
			flow = (@property[:flow] ||= 0)
			to = (@property[:flow_to] ||= v)
			to == v ? cap - flow : cap + flow
		end
	end

	def each_out_connection_of(u)
		u.each_edge{|e|
			yield(e.opposite[u], e.length)
		}
	end

	alias :each_in_connection_of :each_out_connection_of

	def get_augmenting_path(s, t)
		reached = Set[s]
		queue = [s]
		comming_edge = {}
		until queue.empty?
			u = queue.shift
			u.each_edge do |e|	
				v = e.opposite[u]
				next if reached.include?(v)

				next if e.actual_capacity(u) <= 0

				reached << v
				comming_edge[v] = e
				queue << v

				if v == t
					queue = []
					break
				end
			end	
		end

		if comming_edge[t]
			path = [t]
			v = t
			until path[0] == s
				e = comming_edge[v]
				u = e.opposite[v]
				path = [u, e, *path]
				v = u
			end
			return path
		end
		return nil
	end
end

loop do
	n, m, l, s, t = gets.split.map(&:to_i)
	break if n == 0

	g = Graph.new
	nodes = (0..n).map { g.add_node }
	m.times do
		a, b, c = gets.split.map(&:to_i)
		a = 0 if a == s
		b = 0 if b == s
		g.add_edge(nodes[a], nodes[b], {:length => c})
	end

	siros = [[0, 0]] + (1..l).map { gets.split.map(&:to_i) }
	dist = []
	siros.each do |j, e|
		dij = g.dijkstra([nodes[j]])	
		dist << siros.map {|i, f| f + (dij[nodes[i]] || Float::INFINITY)}
	end

	max_num = 0
	hash = { 0 => {0 => 0} }
	(1..2**l-1).each do |visited|
		(1..l).each do |last_idx|
			next if visited[last_idx-1] == 0
			min = Float::INFINITY
			hash[visited - (1 << last_idx-1)].each do |k, d|
				new_d = d + dist[k][last_idx]
				min = new_d if new_d < min
			end
			(hash[visited] ||= {})[last_idx] = min
			return_dist = min + dist[last_idx][0]
			if return_dist <= t
				c = visited.to_s(2).count(?1)
				max_num = c if c > max_num
			else
				hash[visited].delete(last_idx)
			end
		end
	end

	p max_num
end

Measured memory_bytes: 73400