#!/usr/bin/ruby

# Finding Sophie.
# Jan. 2010
# tom.luo@mgail.com

MAX = 1000000
# MAX = 1073741823
locations = []
$min_time = MAX
$probabilities =[]
$connHash = {}
$searched = []

file_name=ARGV[0]
file=File.open(file_name,"r")
$n_locations= file.readline.to_i
$n_locations.times do |i|
 location_probability = file.readline.split(" ") 
 locations << location_probability[0]
 # locations.uniq! "there will be no duplicate names" in the problem statement
 $probabilities << location_probability[1].to_f 
  end

$n_locations.times do |i|
  $n_locations.times do |j|
  $connHash[i] ||= {}
  $connHash[j] ||= {}
  $connHash[i][j] = MAX 
  end
end

$n_conn = file.readline.to_i
$n_conn.times do |i|
  connection = file.readline.split(" ")
  from = locations.index(connection[0])
  to = locations.index(connection[1])
  time = connection[2].to_i
  $connHash[from] ||= {}
  $connHash[to] ||= {}
  $connHash[from][to] = $connHash[to][from] = time
end

 $n_locations.times do |k|
   $n_locations.times do |i|
     $n_locations.times do |j|
        $connHash[i][j] = [$connHash[i][j], $connHash[i][k] + $connHash[k][j]].min if i != j
     end
  end
end

  $n_locations.times do |i| 
   for j in i..($n_locations-1) do 
      if i != j and $connHash[i][j] == MAX  then
         puts "-1.00\n" 
         Process.exit
      end
    end
  end

$n_locations.times do |i|
   $searched[i]=false
end

def search(node, increment, probability)
$searched[node] = true
probability -= $probabilities[node]
finished = true
$n_locations.times do |i|
   if not $searched[i] then
      finished = false
      if ((increment + (probability * $connHash[node][i])) < $min_time) then
         search(i, increment + probability*$connHash[node][i], probability)
      end 
   end
  end
 $searched[node]=false
  if finished then
     if ((increment < $min_time) and ($min_time != -1)) || ($min_time < 0) then
        $min_time = increment 
     end
  end
end

search(0,0,1)
printf("%.2f\n",$min_time)